London advertising agencies: 13 that clients rate for ad work, with costs and what to ask

The leaders matrix gives a summary view of the strongest advertising agencies in this ranking. Each of the 13 agencies is placed on two axes and falls into one of four quadrants: Leaders, Proven, Specialists or Emerging. The size of each dot reflects the size of the agency’s team.

Horizontal axis – track record: the number of verified client reviews, on a logarithmic scale. Vertical axis – focus on advertising: the share of the agency’s reviews that describe advertising work. The dashed lines mark the median of the agencies shown.

1. The sample

Sortlist lists 985 advertising providers on this page. We evaluated the 220 agencies on the first three pages of the listing, in its relevance order. 59 of them have at least 3 verified client reviews – our threshold for a rating to be meaningful. 2 of those also pay for a sponsored placement and were set aside, leaving 57. Of these, 13 agencies with an office in London and at least 3 client reviews that describe advertising work (paid media, ad campaigns, out-of-home) were ranked, with 262 verified reviews between them and an average rating of 4.97; the 44 others are listed separately.

2. The score

3. Independence

• Sortlist is a marketplace, not an agency: it does not appear in its own ranking.
• Agencies cannot pay to enter the ranking or to move up. Agencies with a sponsored placement on this listing are excluded from scoring and shown separately.
• The order of the listing page, subscriptions and badges play no part in the score – only the three criteria above.

4. Limits

Reviews reflect each agency’s work across all its services, and agencies with few reviews may be excellent but are not yet scored. That is why every entry says what it is best for – and when another agency would suit you better. The ranking is updated regularly.

“Advertising” covers very different jobs. We read the 93 reviews of the ranked agencies that describe advertising work and counted which channels they mention. Reviews can mention several, so the columns do not add up.

Use the table to match the agency to the job. A team whose clients talk about Google Ads will not necessarily have the creative range for a launch film, and the reverse is just as true. Ask each shortlisted agency for two examples on the channel you plan to spend most on.

1. 1

   Ask who owns the ad accounts

   Google Ads, Meta Business and TikTok accounts should be opened in your company’s name with the agency added as a user. If the agency runs everything on its own account, you can lose the history when you leave.

2. 2

   Separate the fee from the media spend

   Request a quote with two lines: the agency fee (fixed, or a percentage of spend) and the media budget that goes to the platforms. A percentage fee rises when you spend more, so ask what the cap is.

3. 3

   Fix one number to judge the campaign

   Cost per lead, return on ad spend or cost per acquisition, with the baseline you have today. “More traffic” does not tell you whether the campaign worked.

4. 4

   Ask how many creative variants will be tested

   Platforms reward fresh creative. One published case study on this page reports 480 variants for one retail brand; ask for the number per month you can expect for your budget.

5. 5

   Check which tracking is set up in the first fortnight

   Conversion tracking, consent mode and offline-conversion import should be live before the budget scales. Ask to see the events in the platform, not a screenshot of a report.

6. 6

   Agree the minimum term and the exit

   Several ranked agencies work on monthly rolling terms; others ask for six months. Ask what you keep (accounts, creative files, audiences) if you stop.

7. 7

   Ask who checks the ads against UK advertising rules

   UK ads must follow the ASA’s CAP Code, with extra rules for sectors such as health, finance and gambling. Ask who signs off claims before launch.

Tip: ask every shortlisted agency to read your last three months of ad-account data on a call and tell you the first three things they would change. The answers separate teams that have done this before from those that have not.

Of the 172 London profiles we evaluated, 150 state a minimum project budget. 94 start at €1,000, 8 below that, 5 between €1,001 and €2,999, 14 between €3,000 and €4,999 and 29 at €5,000 or more. These are entry points for a first project, not monthly retainers, and they do not include the media spend.