Top Series A companies in London

Influencer is a global creator marketing agency on a mission to shape the future of marketing by humanizing brands. By placing creators at the center, the agency delivers creator-first solutions across creative, media, and commerce that connect brands with audiences through insight-driven creator campaigns built to stop the scroll and drive measurable impact.Founded in 2015 by YouTuber-turned-entrepreneur Caspar Lee and entrepreneur Ben Jeffries, Influencer is the world’s largest independent creator marketing agency - powered by a unique ecosystem of proprietary technology, platform partnerships, and longstanding talent relationships.As an Official Global Marketing Partner of TikTok, YouTube, Pinterest, Snap, Meta, and Twitch, Influencer delivers bespoke, enterprise-level solutions powered by Waves, its AI-driven operating system. From concept to conversion, the agency blends human instinct with platform intelligence to drive measurable outcomes across the full funnel - from brand perception to performance and sales.With 200+ team members speaking 30 languages across North America, Europe, and the Middle East, Influencer has delivered 6,000+ campaigns for leading brands including Spotify, SharkNinja, Google, Nike, Disney, and Coca-Cola.

• Series A
• 1.4k employees
• Founded 2015

Prolific is a technology company building the biggest pool of quality human data in the world—and the ultimate platform to access it.Over 35,000 AI developers, researchers, and organizations use Prolific to gather data from real, engaged participants—with a new study launched every 2 minutes.Prolific has been ranked among the fastest-growing businesses in the Financial Times 1000 in 2025 & 2024 and the Deloitte Technology Fast 50 in 2023.

• Series A
• 1.4k employees
• Founded 2014

Koru Kids is London’s fastest growing childcare brand. We’re making it easier and more affordable for families to access high quality childcare. Our after school service matches parents in London with the top 10% of student nannies in London and our nanny share service helps families to share nannies with other local families. We don’t just believe in providing outstanding childcare to families, we are all about using technology to make it seamless for parents. We’ve been blown away by the response from parents and are consistently beating our growth targets. We are backed by fantastic investors, including top venture capitalists and business angels such as Michael Pennington the founder of Gumtree. We won the South of England region in the ‘Best of Britain’ awards 2017, and are currently shortlisted for several awards: the UK Business Awards 2017 as ‘Disruptor of the Year’, and in the Best Women Awards 2017 as ‘Best New Business’, ‘Best Technology’ and ‘Best company working with children and families’.About the TeamWe have an informal, hard-working and kind team culture. We’re all passionate about our mission and are determined to create the world’s leading childcare brand. Every team member plays a vital role in achieving our goals and we work together so we can get there quicker. Our approach is fast paced – we are constantly challenging, testing and adapting the way we do things. Our founder is Rachel Carrell, the former CEO of DrThom.com, the world’s largest online doctor service, which she grew to over 1.3m paying users in 3 countries. She’s an Oxford alumn, ex-McKinsey, a Rhodes Scholar and a WEF Young Global Leader. Rachel’s joined by an amazing team with backgrounds including Cambridge, UCL, BCG, KPMG, and some of London’s top startups.

• Series A
• 754 employees
• Founded 2017

Eagle Eye is on a mission to power the personalized marketing revolution globally. Our AI-powered platform combines loyalty and personalization in one place — helping retailers capture rich first-party data, then use it to deliver smarter, 1:1 marketing at scale.It’s real-time, omnichannel, and built for purpose — enabling the world’s leading retail organizations to deliver more value to their customers in a way that’s simpler for their teams to run and better for their bottom line.

• Series A
• 730 employees
• Founded 2003

At Hydrogen Group, we enable people to live healthier, happier, more fulfilling and more successful lives in a rapidly changing world. We do this every day by giving people the tools they need to thrive. We know what works for one person, or business, won’t suit another, but if we can truly understand what type of people will thrive in your business, or what you need to Thrive in your own role, we’ll help you find that person or organisation to help you do just that. Our purpose will ensure that the people we work with are able to thrive, at work and in life. We think this is a big idea that can make life better for our candidates and clients and all people. Hydrogen and Argyll Scott will help people feel good about themselves and help them to understand what success looks like for them, providing clarity and confidence in a changing world. Hydrogen Group is a global award winning, market-leading, specialist recruitment group. Operating a portfolio of brands from offices across nine countries, we support the world’s leading businesses by recruiting the brightest talent. Our specialist teams of around 300 staff know their markets inside out. Last year we enabled the careers of nearly 2,000 people by finding their next permanent move or contracting opportunity, helping them to thrive in our changing world.

• Series A
• 559 employees
• Founded 1997