How to choose a digital marketing agency in the UK (and what to avoid)

Choosing a digital marketing agency has got harder, not easier. There are more agencies and more confident proposals than ever, and most of their websites look equally polished. So here’s the short answer. To choose a digital marketing agency in the UK, start with the commercial result you need, shortlist three or four agencies with proof in a business like yours, and judge them on how they think rather than how they pitch. Then check who’ll actually do the work, how they report, and whether the contract leaves you owning your accounts and data.

The rest of this guide shows you how to do each of those properly: what to look for in a marketing agency, the questions to ask a marketing agency before you sign, and how to run the selection without wasting a month of everyone’s time.

A quick declaration of interest: we’re an agency too, so you can see our services and decide how much salt to add. Everything below is what we’d tell a friend who was hiring someone else.

On this page

• Before you contact any agency
• What to look for in a marketing agency
• Questions to ask a marketing agency
• Cost and contracts
• Full-service or specialist?
• How to run the selection process
• FAQs

What should you decide before you contact any agency?

Decide what success looks like in pounds, roughly what you can spend, and who on your side will own the relationship. Agencies give much better answers to a clear brief, and you’ll spot the weak ones faster when you know what you’re measuring them against.

Write down four things before the first call:

• The commercial goal. “More leads” isn’t a goal. “Forty qualified enquiries a month at under £60 each” is.
• The budget, split in two. Agency fees and media spend (the money that goes to Google, Meta and so on) are different pots. Plenty of businesses quote one number and mean both.
• What’s already in place. Your website, tracking, ad accounts, content and anything that’s been tried and failed.
• Who owns it internally. Someone needs time each month to give feedback, approve work and make decisions.

If you’re wondering what a sensible overall marketing budget looks like, Gartner’s 2025 CMO Spend Survey put the average at 7.7% of company revenue, with half of respondents at 6% or less. It surveyed CMOs, so it leans towards bigger businesses, but it’s a useful sense-check. A firm turning over £3m and spending 5% has £150,000 a year for everything: media, tools, people and agency fees. Knowing that number stops you being sold a plan you can’t sustain past month three.

Why do so many businesses choose the wrong agency?

Most businesses choose the wrong agency because they buy on surface signals like price and polish instead of fit. The relationship rarely fails dramatically. It drifts. Reports arrive, activity is visible, and a year later nobody can say what it achieved.

The usual causes:

• choosing on price before capability
• being impressed by jargon rather than understanding
• picking a channel (“we need SEO”) before agreeing a strategy
• assuming that busy execution means expertise

Each one is understandable. A low quote feels safe, and a confident deck feels competent. The real cost of the wrong agency is the six or twelve months you lose before admitting it isn’t working.

What to look for in a marketing agency

Look for an agency that asks about your business before it sells you services, understands how channels affect each other, shows proof with context, reports honestly and knows how search and advertising work now. Badges and logos help, but they’re the last check, not the first.

They ask about your business before they talk about services

The clearest signal comes in the first conversation. A good agency wants to know where you make money and where you don’t, what’s been tried and why it stalled, what your team can handle internally, and how much risk you’ll tolerate on spend and timelines. If the call jumps straight to packages and platforms, you’re talking to a salesperson with a menu. An agency that hasn’t asked about your margins can’t tell you whether a £40 lead is a bargain or a disaster.

They understand how channels affect each other

Digital marketing doesn’t work in isolation. SEO affects paid media, paid media affects brand search, and your website affects everything. A strong agency asks how things connect, not only how each channel performs on its own. That doesn’t mean you must hire a full-service agency (more on that below). It means whoever you hire should understand what happens either side of their bit.

Their proof matches your situation, with the context left in

Case studies are useful only when you understand what sits behind them. Ask what the starting position was, how long results took, what the budget was, and what went wrong along the way. A headline percentage on a tiny base tells you very little. A good agency will happily talk about what didn’t work and what they changed, and that honesty is worth more than a polished success story. You can see how we present our own work, periods and caveats included, in our case studies.

Relevant proof beats famous logos. If you sell £30 products online, a case study about B2B leads for a law firm shows the agency is capable, not that it can do your job.

They’ve kept up with how search and advertising work now

Years in business matter less than whether the agency has kept up. Search now happens in AI answers as well as blue links, ad platforms automate more of the targeting (Google’s Performance Max can run across YouTube, Display, Search, Discover, Gmail and Maps from a single campaign), and attribution is patchier than it used to be. Ask how they’re handling AI search and what’s changed in their approach in the last 12 months. If the answer sounds like 2019, it probably is. Our guide to AI SEO and GEO explains what “current” looks like in search, and if AI visibility is your main concern there’s a separate guide on how to choose an AI SEO agency.

Their reports explain what happened and why

How an agency reports tells you more than its sales pitch. Ask to see a real (anonymised) monthly report. Good reports explain what happened and why, are honest about what isn’t working, connect activity to business results, and admit uncertainty where it exists. A report that’s all upward arrows and impressions is a warning sign, because no account improves on every line every month.

They’re honest about what nobody controls

Good agencies are confident but realistic. They explain risk, talk about testing phases and set expectations they can defend. Anyone promising guaranteed rankings, fixed costs per lead or predictable returns is oversimplifying, and Google is blunt about this: “No one can guarantee a #1 ranking on Google.” Guarantees are one of several warning signs we cover in our list of 11 red flags when hiring a marketing agency, so we won’t repeat them all here.

Badges and reviews, read properly

Partner badges are worth checking, but know what they mean. To hold the Google Partner badge, an agency needs a 70% optimisation score, $10,000 of ad spend across managed accounts over 90 days, and at least half its account strategists certified. That’s a sensible competence floor. It isn’t proof the agency will do well for you. You can search the Google Partners directory yourself rather than trusting a logo in a footer.

Reviews deserve a closer look too. Read the negative ones and how the agency replied. Since April 2025, fake reviews and concealed incentivised reviews have been a banned practice under UK consumer law, which has made review profiles more trustworthy, but a phone call with a current client still beats any star rating.

Who will actually work on your account?

Ask by name who’ll run your strategy, who’ll do the day-to-day work, and how many other clients each of them handles. Many agencies sell senior expertise and deliver junior execution, and some outsource key work without saying so. Neither is automatically wrong, but you should know before you sign.

Questions that get to the truth:

• Who leads strategy, and who does the hands-on work?
• How many clients does each person on my account look after?
• Is any of the work outsourced or white-labelled? To whom?
• How often will I speak to someone senior?
• What happens when results dip?

Pay attention to how they talk about past clients as well. If you hear a lot of blame, eye-rolling about “difficult clients” or “they never listened”, proceed carefully. You’ll be a past client one day.

What questions should you ask a marketing agency?

Ask questions that reveal how an agency thinks rather than which tools it uses. The quality of the answer matters more than how confidently it’s delivered, and “I don’t know yet, here’s how we’d find out” is often the best answer you’ll hear.

Google’s own advice on hiring an SEO adds a few worth borrowing: ask for examples of previous work, what results they expect and over what timeframe, and how you’ll communicate. The same page also warns you to be wary of agencies that contact you out of the blue, which applies well beyond SEO.

It works both ways. A good agency will also ask you hard questions, and it should be prepared to say no to an idea that doesn’t make sense. An agency that agrees with everything in the first meeting will agree with everything in month six too, including the bad ideas.

How much should a digital marketing agency cost?

There’s no single right price. What matters is whether the fee matches the work needed to hit your goal. Price should be a factor, not the deciding one, and very cheap retainers usually cost more in the long run.

Very low fees usually mean one or more of these:

• junior account management
• templated strategies copied across clients
• little strategic input after the first month
• too many clients per team member

Here’s an illustrative example. Say one agency quotes £500 a month to run £8,000 of Google Ads spend and another quotes £1,500. The cheaper one can afford perhaps a couple of hours a month on your account. If the more expensive agency’s extra time cuts wasted spend by even 15%, that’s £1,200 a month back, which more than covers the £1,000 difference before you count any extra sales. The opposite also happens, of course, which is why you ask exactly what the fee buys: hours, people, deliverables and reviews.

Expensive doesn’t automatically mean good either. Ask for the scope in writing and compare like with like. For paid search specifically, our breakdown of Google Ads management costs shows what typically sits inside a fee.

What should be in the contract?

The contract should give you a reasonable notice period, clear ownership of your accounts, data and creative work, and a proper data processing agreement. Read it before you get excited about the strategy.

Check these points:

• Notice period. Long lock-ins protect the agency, not you. A month or two’s notice is normal for ongoing work.
• Ad accounts in your name. Your Google Ads account should belong to your business, with you holding Admin access, the only level that can grant and remove other users’ access. The same goes for Meta.
• Analytics. In Google Analytics, you need the Administrator role to add or change users. Make sure that’s you, not just the agency.
• Website, domain and creative. Who owns the site files, the domain, the photography and the ad creative if you part company?
• Data protection. If the agency handles your customer data, UK GDPR requires a written contract between controller and processor, including what happens to that data when the contract ends.

Ownership is the one people regret most. Rebuilding an ad account from scratch means losing years of conversion history, and that data is what the platforms’ bidding systems learn from.

Does it matter where the agency is based?

Location matters less than it used to, but it isn’t irrelevant. Most agency work happens remotely now. Still, local knowledge helps with local SEO and regional campaigns, and some businesses simply work better with a team they can meet in person. We’ve written a separate piece on why location still matters when choosing a digital marketing agency, so we’ll leave it there.

Should you choose a full-service agency or a specialist?

Choose a full-service agency when your growth depends on several channels working together and you don’t have an in-house marketing lead to join them up. Choose a specialist when one channel does most of the work, or when you already have someone internally who owns the overall strategy.

Some businesses avoid full-service agencies on the assumption they lack depth. A good one provides integration without diluting the expertise, because specialists still exist within the team and one strategy connects their work. A weak one lists every service on its website and does none of them well. The test is whether the agency leads with strategy or just with a list of services. Our comparison of full-service vs specialist agencies goes into when each one wins.

How should you run the selection process?

Keep it short and structured: a written brief, three or four agencies, a first call each, then proposals from the best two. You’ll learn more from a small paid project or a working session than from a big speculative pitch.

1. Write a one-page brief. Goal, budget, timeline, what’s in place, what’s off-limits.
2. Shortlist three or four agencies. Fewer gives you no comparison. More wastes your time.
3. Hold a first call with each. Count how many questions they ask you. Note who turns up.
4. Check them out. Look up the company on Companies House (are accounts filed on time?), read reviews, and ask to speak to a current client.
5. Ask the best two for a proposal. Give them the same brief and the same access to information.
6. Consider a paid starter project. An audit or a 90-day plan shows you how they really work.
7. Score them on the same criteria. Strategy, relevant proof, people, reporting, contract terms and fit.

On free pitches: they’re not as free as they look. The IPA says clients think a large “no frills” pitch costs an agency about £31,000, when the reality is closer to £178,000, roughly 90 working days. That’s big-agency territory, but the principle holds at any size. Agencies price pitching into their fees somewhere, and the IPA and ISBA’s Good Pitch guidance encourages a fair, transparent process with clearly defined stages for exactly that reason.

Why do agency relationships succeed or fail?

Agency relationships succeed when both sides agree who does what and what counts as success. They fail when expectations stay vague. Even a good agency struggles with a fuzzy brief.

That cuts both ways. In a 2018 study by the World Federation of Advertisers, agencies said collaboration was held back by clients’ internal structures (51%), poor briefs (49%) and a lack of trained client staff (40%). Those were large multinationals, but the pattern turns up in businesses of every size. If approvals take three weeks, your campaigns will be three weeks late.

The partnerships that work best are collaborative rather than transactional. The agency understands the business, the business trusts the process, and both can say “this isn’t working” without it turning into a row. A marketing agency should feel like an extension of your team, not an external supplier you chase for updates.

How Castle works with clients

At Castle, strategy comes before execution, channels are connected on purpose, and reporting explains what’s happening rather than just listing activity. We’re a digital marketing agency in Liverpool with 25 UK-based staff, working with businesses across the UK.

In practice that means a rolling monthly agreement with no tie-in, onboarding that usually takes about a week, and plain-English reporting on what’s working, what needs changing and why. Some of our relationships run for years. We’ve worked with Clatterbridge Private Clinic continuously since 2018, across 15 disciplines. We’d still rather you chose us because the fit is right than because the contract made leaving awkward.

Choosing a digital marketing agency is a big decision, and the right partner should make growth clearer, not more complicated. If you’d like a second opinion on a shortlist or a proposal you’ve already been sent, talk to our team.

FAQs

How many agencies should I shortlist?

Three or four is usually right. That’s enough to compare approaches and prices without turning selection into a second job. Hold a first call with each, then ask the strongest two for a written proposal against the same brief.

How long before I see results from a new agency?

It depends on the channel. Paid search and paid social can show early signals within weeks, while SEO usually takes several months to build. Expect the first month to go on onboarding, tracking and fixes. Be cautious of anyone promising dramatic results in the first 30 days.

Should I sign a 12-month contract?

We’d avoid it unless there’s a good reason, such as a large build project with staged payments. A shorter notice period keeps both sides honest. If an agency insists on a long lock-in for ongoing marketing, ask why it needs one.

What’s the difference between a marketing agency and a digital marketing agency?

A digital marketing agency focuses on online channels such as search, paid social, websites, email and content. A broader marketing agency may also handle PR, print, events or TV. Most UK businesses now need mainly digital, with offline work where it genuinely helps.

Is a bigger agency always better?

No. Bigger agencies bring more resources and specialists, but your account may be a small fish in a big pond. Smaller agencies can give you more senior attention but less depth. Judge on who will actually do the work and how much of their time you’ll get.