Experience Engineer (FTC) in London, United Kingdom

The Experience team owns the human-facing side of Callsign: the client portal, our demo and client management platform (one platform for the whole client journey, from first demo through proof of concept, onboarding, integration, analysis and ongoing management), the data-product UIs, and the design system and engineering standards behind all of it.

This position is offered as a 12 month fixed-term contract with the successful candidate ideally joining in 2026.

The candidate will already need to hold the right to work in the UK.

What you’ll do:

Product & UX:

• Own features end-to-end, from ambiguous requirements to shipped experience: fills design gaps with defensible decisions and delivers a coherent flow rather than a set of components
• Contribute actively in refinement: challenge requirements with evidence, propose simpler alternatives, and bring product ideas of your own
• Know the outcome each feature serves, instruments what they ship so that outcome is measurable, and checks whether it landed (usage, feedback, demo performance) rather than stopping at merge
• Understand the domain the product lives in (fraud, identity, authentication, and the client's operational world) well enough so that gap-filling decisions reflect

Frontend craft:

• Implement non-trivial components and async data flows
• Diagnose and fix performance and accessibility issues rather than merely detecting them
• Handle secrets/config surfaces safely

Full-stack

• Ship features that span frontend, backend service and configuration
• Debug across the boundary to root cause
• Significant changes start as a written design others can review, rather than as code

Quality

• Design the test approach for your features (what gets unit, component and e2e coverage, and why)
• Keep regression suites healthy in your area; e2e failures you own get fixed rather than retried

Platform:

• Land toolchain and pipeline improvements (build config, CI automation, test infra, dependency upgrades) beyond your immediate feature work.

Requirements

Key Responsibilities

• Ship across the stack: TypeScript/React frontends, Node services (with some Java in the portal estate), API contracts, GitLab CI/CD, and deployment via Helm, GitOps and Terraform.
• Treat the frontend craft triad - accessibility, performance, security - as engineering, with expectations that rise as you grow.
• Build with AI as a core part of your workflow, with the verification discipline a regulated product demands.
• Learn the domain deliberately: fraud, identity, authentication, and our clients' operational world, because product decisions made without it are guesses.
• Write meaningful tests for everything you ship.

Required Skills & Experience

A must:

• Solid JavaScript/TypeScript and React.
• Comfort somewhere beyond the frontend: an API, a service, or infrastructure.
• System design and architecture, designing features that span frontend, service and configuration.
• Evidence of AI-native working with stated verification.
• A testing instinct: you can design a test approach and defend it.

Would be great:

• Product judgement demonstrable from your history: UX decisions made and defended without a design spec.
• Ownership of a surface or programme through its worst weeks, at any scale.

Nice to have:

• Java in production; design systems or component library work; SDK or library engineering; data visualisation
• Experience in regulated industries (fintech, identity, payments).

Benefits

Pension scheme with Scottish Widows

Private medical cover with Vitality

Life assurance (4x base salary)

Personal Learning & Development Budget

Cycle to Work Scheme

Company Family Leave

25 days annual leave plus Callsign Bank Holiday

Employee Volunteering Program