Artificial Intelligence jobs in United Kingdom

Can you help us fix the world’s most broken supply chain? The fashion industry produces over 100 billion garments a year. 60% end up in landfill — not because people don’t want these clothes, but because the supply chain for getting secondhand fashion from donation to resale is completely offline, manual, and broken.

Fleek is fixing this. Our mission is to make secondhand the first choice. We’re building the infrastructure powering the global secondhand clothing trade — through a B2B marketplace and the AI systems digitising the supply chain behind it.

Through Fleek, vintage stores, online resellers, and retail buyers source graded secondhand inventory directly from wholesalers and rag houses across multiple countries. Our key enabler is FleekSort — an AI model fine-tuned on secondhand fashion — that can grade, price, and categorise items with just a photo, turning what has historically been an opaque and manual trade into a structured, searchable, and tradable global inventory layer.

Since 2022, we’ve saved 9 million items from landfill and tripled in size year-on-year. We’ve raised ~\$50M from a16z, Y Combinator, Burda Principal Investments, HV Capital, and others, and have recently closed our Series B. Our advisors and private investors include operators behind Depop, Shopify, and Postmates.

Today, we serve thousands of resellers and retailers across the UK, Europe, and the US. With the secondhand fashion market projected to reach $350B by 2027, Fleek is building the AI-native operational and financial backbone for secondhand commerce globally.

We’re looking for people who want to build something that matters — and move fast doing it. Sound good? Keep reading.

This is a Senior Backend Engineer role in Fleek’s product engineering team. You’ll report into our CTO, Sanket Agarwal (ex-Google, Postmates), and work embedded with a product manager and designer in a small, senior squad focused on the core marketplace experience.

Fleek is digitising an industry that has never had technology. There are no existing playbooks for building an ecommerce experience around secondhand fashion at wholesale scale — where every item is unique, inventory is unpredictable, quality is graded by AI, and the supply chain spans three continents. You will be designing how the transaction layer works for a market that hasn’t existed before.

You will be on our Growth team, owning the ecommerce journey from discovery to checkout, payment and credit systems, order management, and seller tools. Your systems will handle 500,000+ items a month today and million+ by the end of the year.

AI is at the core of everything we do, so you’ll work closely with our data and AI teams to build the backend services that connect FleekSort’s classification engine to the marketplace experience.

We’re looking for a product engineer who can think about how systems affect buyers and sellers at scale. You’ll be expected to understand the business problems your code solves — and challenge whether we’re solving the right ones.

• Product-Obsessed Builder: You think about what the seller sees when their inventory goes live, or why a buyer drops off at checkout. You instinctively connect technical decisions to commercial outcomes.
• Comfortable with Ambiguity: We’re building systems for workflows that didn’t exist before Fleek. You thrive when the problem is undefined and collaboration is key.
• Customer-Focused Thinker: You understand the dynamics of customer platforms and can understand how technical choices affect customers and our broader marketplace.
• Owner, Not Renter: You take a feature from problem definition to production and monitor it afterwards.
• Startup Pace: You’ve worked in environments where shipping matters more than perfection, where you deploy daily, and where velocity is a competitive advantage.

• Own the Ecommerce Journey: Design and build the backend systems powering Fleek’s core marketplace — from item discovery and search through to checkout, payment, and post-purchase. These are product features that directly drive GMV.
• Integrate AI into the Product: Build the services that connect FleekSort’s AI classification engine to the marketplace experience — ensuring grading, pricing, and categorisation flow seamlessly into listings, search, and buyer workflows.
• Design for Scale: Architect systems that handle 500K+ items per month today, with a clear path to millions. Make pragmatic trade-offs between speed of delivery and long-term scalability.
• Shape Technical Direction: Contribute to architectural decisions across the backend. Challenge assumptions, propose alternatives, and help define engineering standards for a fast-growing team.
• Mentor and Elevate: Support the growth of more junior engineers through code reviews, pairing, and knowledge sharing. Help raise the technical bar across the team.
• Collaborate Cross-Functionally: Work embedded with your product manager and designer to define what gets built. Partner with data, AI, and operations teams to turn complex real-world logistics into reliable, scalable software.

• 3–6 years of professional backend engineering experience: You’ve built and shipped production systems that handle real traffic and real money.
• Strong fundamentals in system design, data modelling, and API architecture: You can design a service from scratch and reason about its failure modes before you write a line of code.
• Experience with Node.js and TypeScript (our primary backend stack), or strong proficiency in a comparable stack with willingness to transition.
• Consumer tech background: You’ve worked at a marketplace, fintech, or consumer product company. You understand what it means to build for end users at scale, not internal tooling or enterprise workflows.
• Product engineering mindset: You can articulate the business problem your code solves. You’ve worked closely with product and design, and you’ve made trade-offs that balanced user experience with technical constraints.
• Startup or scale-up experience: You’ve worked in environments with fast deployment cycles, evolving requirements, and high ownership. You ship, learn, and iterate.
• Comfort with ambiguity: You don’t need a detailed spec to start moving. You can take a problem statement and turn it into a working system.
• AI first 10x-er: You think about your role as a 10x-er through the lens of AI. You’ve built AI capabilities either in your spare time or in deployment at scale.

• Experience with marketplace dynamics: two-sided platforms, pricing, trust, supply-demand matching
• Familiarity with international systems and distributed teams across multiple time zones

A genuine excitement for building something from scratch in a category that didn’t exist three years ago.

• Narrow, siloed ownership where you only touch one service and never see the user
• Detailed specs handed to you before you start — we define problems together
• A slow-moving, highly structured environment with long release cycles
• Fully remote work — this team is on-site in London five days a week
• Pure infrastructure or platform work with no product exposure

Ready to build the infrastructure for the world’s fastest-growing fashion economy? If you want to work on genuinely hard problems, with a world-class team, at a company that’s tripling annually — we’d love to hear from you.

• Location: London HQ — Heneage Street, E1 (Shoreditch / Aldgate East)
• Work model: On-site, five days per week
• Level: Senior (L5)
• Stage: Post-Series B, hyper-growth
• Team: 100+ across London, India, and Pakistan
• Stack: Node.js, TypeScript, AI/ML integration
• Culture: High ownership, non-hierarchical, fast-moving. Founder-led with strong opinions loosely held.

Fleek is building the AI-native operational and financial backbone for a $350 billion market that has never been digitised. Joining now means you’ll be part of the team that defines how the secondhand economy works — at scale, globally.

• The problem is real: 9 million items saved from landfill since 2022. Your work has tangible, measurable impact.
• The AI is genuinely novel: FleekSort is an AI model fine-tuned on secondhand fashion, turning an opaque manual trade into a structured global inventory layer. This isn’t a GPT wrapper.
• The growth is exceptional: Tripling year-on-year, ~\$50M raised, Series B closed. Backed by a16z, Y Combinator, HV Capital, with advisors from Depop, Shopify, and Postmates.
• The timing is perfect: The secondhand market is projected to reach $350B by 2027. EU regulation is mandating the infrastructure Fleek builds. You’re catching a wave.
• You’ll have real ownership: 100-person company, no bureaucracy. You’ll shape decisions and see the impact of your work immediately.

Five values shape how we work at Fleek:

• Dream Big and Disrupt Yourself: Push the most ambitious version of what you’re building. Step out of your comfort zone. Nothing is out of reach.
• Absolute Ownership: The buck stops with you. Drive initiatives to completion. Experiment, learn, persevere. The job isn’t done until the job is done.
• Curiosity Leads the Way: Don’t accept anything at face value. Ask questions you don’t know the answer to. That’s how you innovate.
• Talk to the Customer: Deeply understand their challenges, motivations, and ambitions. Every decision starts with the customer at the centre.
• Embrace Diversity: A global team building for a global supply chain. Bring your authentic self and embrace the diversity of everyone you encounter.