Table of contents
How we vet every listicle
Every agency featured on Web Tonic passes our 84-point editorial review before a single listicle goes live. This is how we vet each pick:
Verified client outcomes: We require real case studies with measurable KPIs — revenue, ROAS, CPA, retention — tied to the exact category being ranked. No cherry-picked wins, no unverifiable numbers.
Independent reputation: We cross-check Clutch, Google, G2, and Trustpilot ratings, and screen for review-bombing or suspicious patterns. Only operators with a consistent, verifiable track record make the cut.
Beyond that, every listing goes through a quarterly re-audit. We check 84 criteria across 6 pillars to make sure it still holds up — here are some of the checks we run:
A conversion rate optimization agency works on traffic you already pay for: it instruments the site, reads where visitors abandon, turns each guess into a written hypothesis, then proves or kills it with a controlled A/B or multivariate test before the winning version is built for good.
Our screen was deliberately narrow: twelve external firms serving London survived it, judged on testing and analytics work shown on their own sites rather than a CRO line in a services menu. Several here are ecommerce build shops that test what they ship, which is a different offer to a pure experimentation team.
What does a London conversion rate optimization agency actually deliver?
Research, instrumentation, written hypotheses and tested changes to the pages your traffic already lands on. Twelve external firms working in London cleared our evidence read; eleven publish a London address, three credit a client you can check, and none prints a rate.
1. Web Tonic
About: Web Tonic runs testing inside the growth program rather than as a side project, so the measurement work, the paid traffic that fills the page and the build that ships a winning variant are briefed together. Briefs from London usually arrive with plenty of sessions and no test history, so the first session is spent on what that traffic can actually prove
Key Services: Growth Marketing, Paid Social, PPC, Meta Ads, SEO, Google Ads, Snapchat Ads, Amazon Ads, Reddit Ads, TikTok Ads, TikTok Shop, GEO-AEO, Webflow Design, Shopify Design, WordPress Design, UGC, Social Media Management, Pay Per Click Management, Marketing Analytics, Analytics Implementation & CDPs, Performance Branding, Performance 360° Audit, Programmatic Ads, OOH Ads, HR Marketing
Industries Served: eCommerce, SaaS, B2B, Construction Professionals, Home Services, SMEs, Health Spa & Wellness, Retail, Legal & Judicial Services, Food & Beverages, Pets, Fitness, Family & Children, Finance & Insurance, Travel, Non-Profits & Organizations, Furniture & Decoration
Notable Clients: WorldRemit, Jack & Jones, Ardene, L’Oréal, Sendwave, Nestlé, Airbnb. Serve Fortune 500 companies and smaller fast-paced startups.
Locations: HQ in San Francisco with notable offices in New York, Chicago, Miami, Toronto, Montreal, Dubai, Singapore, Sydney and more. Offices on five continents.
Pricing: Starting at USD $3,000 per month. Flexible and scalable plans at any time according to your enterprise needs. Book a call to learn more.
Great For: Mid-market to enterprise-level businesses requiring ongoing, on-tap growth and performance marketing services.
Website: Web Tonic
2. Pearl Lemon
About: Pearl Lemon provides expert conversion rate optimization (CRO) and experimentation services designed to improve online performance, user onboarding, and funnel conversion rates. They utilize behavioural analytics, UX principles, and rigorous A/B testing methodologies to identify and resolve conversion obstacles for businesses.
Key Services: Conversion Rate Optimization (CRO), A/B and Multivariate Testing, UX & Behavioural Analytics, Heuristic Evaluation & Hypothesis Mapping, Search Engine Optimization (SEO), Lead Generation
Industries Served: E-commerce, SaaS, Finance, Healthcare, Legal, Retail, Professional Services
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: E-commerce brands, SaaS brands, Finance brands
Website: Pearl Lemon
3. Charle Agency
About: Charle Agency is a London-based Shopify Plus partner agency specializing in design, development, and conversion rate optimization for e-commerce brands. Their work focuses on enhancing online storefront experiences and driving performance for direct-to-consumer merchants.
Key Services: E-commerce Design, E-commerce Development, Shopify Plus Expert Services, Conversion Rate Optimization
Industries Served: E-commerce, Retail, Direct-to-Consumer (DTC)
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: E-commerce brands, Retail brands, Direct-to-Consumer (DTC) brands
Website: Charle Agency
4. Avex E-commerce Agency
About: Avex is a New York City-based digital agency specializing in e-commerce design, development, and conversion rate optimization for lifestyle and luxury brands. They build and optimize Shopify Plus digital flagships using a data-driven approach to enhance user experience and scale revenue.
Key Services: E-commerce Development, Shopify Plus Development, Conversion Rate Optimization (CRO), UI/UX Design, Digital Strategy, Email Marketing
Industries Served: Fashion, Beauty, Luxury, Lifestyle, E-commerce
Notable Clients: No client publicly named on the firm's own site
Locations: New York, United States
Pricing: Quote-based
Great For: Fashion brands, Beauty brands, Luxury brands
Website: Avex E-commerce Agency
5. Genie Crawl
About: Genie Crawl is a boutique digital marketing and SEO agency based in London, United Kingdom. They specialize in services such as search engine optimisation, PPC management, lead generation, and online reputation management. They operate on a rolling monthly basis to provide flexible digital marketing solutions.
Key Services: SEO Services, Pay Per Click Management, Link Building Optimisation, Lead Generation, Website Development, Online Reputation Management
Industries Served: Not publicly stated
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: Local and regional brands
Website: Genie Crawl
6. Elevate Digital
About: Elevate Digital Solutions is a London-based digital marketing agency focused on driving profitability and performance for eCommerce and service brands. They specialize in conversion rate optimization (CRO), data-backed A/B testing, pre- and post-click optimization, and SEO to enhance user journeys and scale revenue.
Key Services: Conversion Rate Optimization (CRO), A/B Testing, Pre-Click & Post-Click Optimization, Quantitative & Qualitative Analysis, SEO, PPC, Website Design & Development
Industries Served: eCommerce, Service Brands
Notable Clients: World Surgery Tour
Locations: London
Pricing: Quote-based
Great For: eCommerce brands, Service Brands brands
Website: Elevate Digital
7. Gripped
About: Gripped is a specialist B2B digital marketing agency based in London that integrates search, content, paid media, and conversion optimisation into a cohesive strategy for software companies. They focus on turning traffic into qualified pipeline and revenue through structured website development and CRO initiatives tailored for B2B tech brands.
Key Services: Conversion Rate Optimization (CRO), Demand Generation Strategy, Paid Media, SEO, GEO (Generative Engine Optimization), Website Development
Industries Served: B2B SaaS, AI, Tech
Notable Clients: Ideagen, Epicor, Ravelin, Crownpeak
Locations: London
Pricing: Quote-based
Great For: B2B SaaS brands, AI brands, Tech brands
Website: Gripped
8. Passionate Agency – Passionates
About: Passionate Agency – Passionates is a London-based digital and web design agency offering subscription and project-based creative solutions. Their services explicitly include post-launch conversion optimization alongside UI/UX design, web development, and brand strategy to help turn qualified traffic into business pipeline.
Key Services: Conversion Rate Optimization (CRO), Web Design, UI/UX Design, Graphic Design, Branding, Web Development
Industries Served: B2B, Technology, Professional Services, SaaS, Financial Services
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: B2B brands, Technology brands, Professional Services brands
Website: Passionate Agency – Passionates
9. Opefir Agency
About: Opefir Agency LTD is a conversion optimization and digital agency registered in the UK that focuses on maximizing store conversions, increasing average order value, and scaling e-commerce brands. Their core offerings combine technical development expertise with tailored optimization solutions to improve digital performance.
Key Services: Conversion Rate Optimization (CRO), A/B Testing, E-Commerce Development, Shopify Optimization, Store Automation, Web Development
Industries Served: E-commerce, Retail, Fashion, B2B
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: E-commerce brands, Retail brands, Fashion brands
Website: Opefir Agency
10. Found
About: Found is a London-based digital marketing agency that offers comprehensive conversion rate optimisation (CRO) and A/B testing services. Their approach uses data-backed insights and experimentation to remove user journey friction and maximize existing website traffic.
Key Services: Conversion Rate Optimisation (CRO), A/B Testing, SEO, PPC, Paid Social, Data & Analytics, Content Marketing
Industries Served: Ecommerce, Hospitality, Travel, B2B, Financial & Professional, SaaS, Fintech
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: Ecommerce brands, Hospitality brands, Travel brands
Website: Found
11. OptiExperts
About: OptiExperts is a London-based certified Shopify Plus partner agency specializing in data-driven e-commerce growth, conversion rate optimization (CRO), and A/B testing. They combine technical Shopify development with user behavior analysis to maximize conversion rates, average order values, and overall store performance.
Key Services: Conversion Rate Optimization (CRO), Shopify Plus Development, A/B Testing, UI/UX Design, Store Speed Optimization, Shopify Migrations, Custom App Development
Industries Served: Fashion, Beauty, Food, Lifestyle, DTC E-commerce
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: Fashion brands, Beauty brands, Food brands
Website: OptiExperts
12. Medito Digital
About: Medito Digital is a Shopify expert agency headquartered in London that delivers conversion rate optimization, user experience refinement, and A/B testing strategies. Their data-driven CRO approach focuses on analyzing user behavior, heatmaps, and checkout optimization to maximize e-commerce sales.
Key Services: Conversion Rate Optimisation (CRO), A/B Testing, Shopify Theme Development, Shopify Migration, Klaviyo Email Marketing, Shopify Speed Optimisation
Industries Served: E-commerce, DTC, Fashion, Lifestyle
Notable Clients: Dior
Locations: London
Pricing: Quote-based
Great For: E-commerce brands, DTC brands, Fashion brands
Website: Medito Digital
13. EXENLABS
About: Exen Labs is a fully in-house Shopify agency based in London that partners with brands to design, build, and grow online stores. They provide senior-led delivery ranging from store setup and custom development to ongoing conversion rate optimization (CRO), SEO, and digital marketing growth programmes.
Key Services: Shopify Store Setup, Custom Feature Development, Site Speed Optimisation, Search Engine Optimisation (SEO), Conversion Rate Optimization (CRO), Paid Media & Marketing Programmes
Industries Served: Ecommerce, Retail, Luxury Menswear, Cosmetics
Notable Clients: No client publicly named on the firm's own site
Locations: London
Pricing: Quote-based
Great For: Ecommerce brands, Retail brands, Luxury Menswear brands
Website: EXENLABS
Quick Comparison Table
| Agency | Key Specialty | Starting Price | Best For |
|---|---|---|---|
| 1. Web Tonic | Full-Service Performance Marketing | USD $3,000/mo | Mid-market to Enterprise |
| 2. Pearl Lemon | Conversion Rate Optimization (CRO) | Quote-based | E-commerce brands |
| 3. Charle Agency | E-commerce Design | Quote-based | E-commerce brands |
| 4. Avex E-commerce Agency | E-commerce Development | Quote-based | Fashion brands |
| 5. Genie Crawl | SEO Services | Quote-based | Local and regional brands |
| 6. Elevate Digital | Conversion Rate Optimization (CRO) | Quote-based | eCommerce brands |
| 7. Gripped | Conversion Rate Optimization (CRO) | Quote-based | B2B SaaS brands |
| 8. Passionate Agency – Passionates | Conversion Rate Optimization (CRO) | Quote-based | B2B brands |
| 9. Opefir Agency | Conversion Rate Optimization (CRO) | Quote-based | E-commerce brands |
| 10. Found | Conversion Rate Optimisation (CRO) | Quote-based | Ecommerce brands |
| 11. OptiExperts | Conversion Rate Optimization (CRO) | Quote-based | Fashion brands |
| 12. Medito Digital | Conversion Rate Optimisation (CRO) | Quote-based | E-commerce brands |
| 13. EXENLABS | Shopify Store Setup | Quote-based | Ecommerce brands |
Frequently Asked Questions
What sits inside a London conversion rate optimization engagement?
Four parts, and each belongs on its own line of the quote. Research comes first: analytics review, session recordings, heatmaps and whatever user testing the budget allows. Hypotheses follow, written so a result can settle them. Testing is third, which is where sample size, test duration and statistical significance decide whether you learn anything. Implementation is fourth, because a winning variant that never ships is a report, not a gain.
Why does this shortlist stop at twelve external firms?
Because the evidence bar removed everyone else. We started from the agencies a London search surfaces, then read each site for conversion work on the record: testing programs described, experiment tooling named, optimisation service pages that load, and a logo of their own rather than stock art. Firms selling CRO only as a bullet under web design, and sites we could not fetch, were cut. Nothing was added to round the number up.
Which of these agencies name clients I can verify?
Three of the twelve. Elevate Digital names World Surgery Tour, Gripped names Ideagen and Epicor, and Medito Digital names Dior. The rest credit nobody on the pages we read, which under a confidentiality clause is ordinary rather than suspicious, though it pushes references into the first call. Ask for two tests in your own category, including one that lost, and for the numbers behind both.
How do I compare quotes when nobody publishes pricing?
Fix the deliverables before you read a figure. Since no firm here prints a rate, bids only become comparable once you have set how many tests run per month, who writes the hypotheses, whether development and design of each variant are included, which analytics and testing tools you pay for directly, how results are reported, and what happens to a winner. Two bids on one brief routinely differ threefold on those lines.
Do I have enough traffic, and does the agency need to be in London?
Traffic decides more than geography. A test needs enough conversions per variant to settle inside a few weeks, so low-volume sites are better served by research, qualitative testing and outright redesign than by a split-testing retainer. Eleven of the twelve firms publish a London address and the rest sell into the city from elsewhere: Avex E-commerce Agency (New York, United States). Proximity helps while the research is being argued out, and matters little once tests are running.
Choosing a Conversion Rate Optimization Partner in London
Eleven of the twelve external firms here publish a London address, so geography alone will not shorten this list. What separates them is whether experimentation is the core craft or a service sold under a website build.
Three credit a client you can check, and not one prints a rate. Settle how many tests a month you are buying, and who builds the winning variant, before you collect quotes.
Programs fail on volume and on implementation, rarely on ideas. Ask what conversion volume your pages need for a valid test, how long each one runs, and who ships the winner into the live site.
Whoever takes the brief, read the research plan and the reporting together, because a test with no hypothesis behind it is decoration. If you would rather hold measurement, testing and the growth program in one place, read our latest analysis or see how we work in London.
