CRO Agencies in London: 6 With a Real Office (2026)

London had 1.042 million private sector businesses at the start of 2025, more than any other UK region, according to the Department for Business and Trade.

It also has more pages claiming to be “London’s leading CRO agency” than any shortlist needs. Many are directories, and some are agencies ranking themselves first.

So we checked each candidate’s own site for a London street address and a CRO service it explains. Six passed. One more listed a City Road virtual office as its only address, so it’s not here.

Which London CRO agency fits your business?

The best CRO agencies in London in 2026 are Conversion, Conversion Rate Experts, AWA Digital, Lean Convert, ClickSlice and Underwaterpistol. Four do CRO as their main business; two pair it with SEO or Shopify builds.

• Enterprise experimentation: Conversion, Southwark
• A proven method for fast-growing firms: Conversion Rate Experts, Fitzrovia
• Online retail with a senior lead: AWA Digital, Fitzrovia
• Building a testing culture in-house: Lean Convert, Bloomsbury
• Search traffic that should sell more: ClickSlice, Hoxton
• Shopify Plus stores on a results-based fee: Underwaterpistol, Soho

London CRO agencies compared

Three of the six open with something free. None publishes a monthly CRO price, and one ties its fee to results.

The 6 London CRO agencies we verified

Each profile gives a one-line verdict, three facts from the agency’s own site, and one question worth asking on the first call.

1. Conversion: Enterprise Experiments

Verdict: the safest pick for large brands that want experimentation run as a programme, not a project.

• Known for: Conversion designs, builds and analyses every test itself, and extends into personalisation and even product and pricing experiments.
• Proof: Dollar Shave Club, Meta and Microsoft appear among its clients, and it credits its work with more than $2 billion in extra client revenue.
• Office: Valentine Place, Southwark, with a second base in Vancouver. It is part of the GAIN group.

Ask them: who on their side owns our programme week to week, and how often do we meet them?

2. Conversion Rate Experts: Method

Verdict: a long-established team for businesses that want every change proven by an A/B test before it counts.

• Known for: Conversion Rate Experts works to its own CRE Methodology and insists on scientific tests to verify results.
• Proof: it names Amazon, Apple, Google, Facebook and Dropbox as companies it has helped grow, across 41 countries and 11 languages.
• First step: a free strategy session, offered to businesses making over $1m online.

Ask them: which of our pages would you test first, and what result would make it worth continuing?

3. AWA Digital: Ecommerce CRO

Verdict: a specialist built for online retailers who want a senior person on the account from day one.

• Known for: AWA Digital puts a specialist with 7+ years of direct experience in charge of every programme.
• Proof: two “CRO Agency of the Year” awards and thousands of A/B tests across hundreds of sites and apps.
• Office: Mortimer House in Fitzrovia, plus York, Austin and Cape Town. A free two-minute benchmark report is the usual opener.

Ask them: will the senior specialist who pitches us also run our tests?

4. Lean Convert: Testing Culture

Verdict: the pick for teams that want to learn how to experiment, not just receive results.

• Known for: Lean Convert combines experimentation, CX optimisation, personalisation, research and analytics, framed around four questions that start with “What is the hypothesis?”
• Proof: case studies include Expensify and a client that gained £500k in incremental revenue within weeks.
• Office: Lynton House on Tavistock Square, Bloomsbury, with team members spread across Europe and the US.

Ask them: how will our own team be involved, so we can keep testing after you step back?

5. ClickSlice: SEO Plus CRO

Verdict: a good fit when search already brings visitors and the site isn’t turning them into sales.

• Known for: ClickSlice is an SEO-led agency whose CRO service uses A/B testing, heat mapping and behaviour analysis on landing pages.
• Proof: its CRO page centres on ecommerce and landing page work alongside its search campaigns.
• Office: Shoreditch Stables on Kingsland Road, Hoxton. A free video audit starts things off.

Ask them: will CRO and SEO share one report, or will we get two separate ones?

6. Underwaterpistol: Shopify Plus

Verdict: the lowest-risk way for a Shopify Plus brand to start, because part of the fee depends on results.

• Known for: Underwaterpistol runs a performance-based CRO model, moving from customer insights to hypotheses, then A/B and multivariate tests.
• Proof: pet food brand Pooch & Mutt saw conversion rise 41% and revenue 36% after a navigation rebuild.
• Office: Wardour Street, Soho. It also builds and migrates Shopify Plus stores.

Ask them: how exactly is “results” measured in the fee, and over what period?

Specialist CRO firm or SEO-led agency?

London’s six split into two camps, and the right one depends on where your problem sits.

• Pick a specialist if traffic is steady but too few visitors act. Conversion, Conversion Rate Experts, AWA Digital and Lean Convert treat testing as the whole job.
• Pick an SEO-led or build agency if traffic itself is thin, or your store needs rebuilding. ClickSlice and Underwaterpistol cover both sides.
• Check who builds the variants. A specialist that codes tests saves your developers time; one that only advises adds work to their queue.
• Compare the first month. Ask each agency for a written plan before you sign, so you can see research, tests and reporting side by side.

What the 2026 cookie changes mean for testing

Testing tools and analytics rely on cookies, and UK rules on those changed this year.

The Data (Use and Access) Act 2025, passed in June 2025, allows some storage and access technologies without explicit consent in low-risk situations. Most provisions took effect in February 2026, according to NI Business Info.

• Ask what your tools qualify for. Whether a given analytics or testing setup fits the new exceptions depends on how it is configured, so get a clear answer in writing.
• Know who drops out. Visitors who decline consent may not be counted, which shrinks the sample a test can use.
• Plan for longer tests. A smaller counted audience means each test needs more time to reach a clear result.
• Keep advice separate. An agency can explain its setup, but your own legal adviser should sign off on consent decisions.

How to spot a London page with no London office

Searches for London CRO agencies return plenty of pages from firms that have never had a desk in the capital. Each of these checks takes a minute or two.

• Find a street address. A list of cities in a footer is not an office, and some addresses belong to virtual office services shared by many firms.
• Read the CRO page. A real service explains how tests are chosen, built and measured.
• Watch for self-ranked lists. A “best agencies” article that puts its own publisher first is marketing, not a review.
• Check the dates. Blog posts and case studies stamped within the past year and a half suggest the team is still trading.

WiserNotify publishes this guide. A London CRO agency might trial its live sales and visitor pop-ups as a trust cue on a product or landing page.

Wrap Up

Choose the label that matches your business, ask each agency the question in its profile, and compare two written plans for month one.

Comparing UK firms with overseas ones? Try our worldwide best conversion rate optimization agencies shortlist.

Other UK locations

• CRO agencies in Birmingham
• CRO agencies in Manchester
• CRO agencies in Newcastle