Principal Lead Contractor in London

The Principal Lead provides technical leadership across six engineering capabilities: SAP, DevOps, Domain Services, Storefront, iOS and Android. Working between the Capability Leads and the Architecture team, they provide hands-on technical leadership and design support as a full-stack engineer, and are accountable for raising engineering standards and defining, building and embedding best-of-breed practices that make secure software development and built-in observability the default. They also act as the senior point of technical escalation, taking the lead to resolve issues where Engineers, Technical Leads or Capability Leads are stuck. The Principal Lead will also lead the introduction of agentic development practices across the engineering organisation, moving teams beyond AI code completion towards AI agents that plan, build, test and review changes under clear human oversight. They work in close partnership with the Capability Leads, the Architecture team and the Engineering Manager to make good practice the default way of working, and to leave practices, standards and knowledge firmly embedded in the teams by the end of the engagement. This is a contract position.

Accountabilities & Responsibilities

• Define, build and embed best-of-breed engineering practices across all six capabilities: SAP, DevOps, Domain Services, Storefront, iOS and Android.
• Act as the senior technical escalation point; take the lead and drive resolution where Engineers, Technical Leads or Capability Leads are blocked.
• Provide hands-on technical leadership and contribute to solution design as a full-stack engineer, working alongside the Capability Leads and Architecture team.
• Lead the design and rollout of agentic development practices across the engineering organisation, covering planning, coding, testing, security, release and operations.
• Define guardrails and responsible-use standards for agentic and AI-assisted engineering, including tools such as GitHub Copilot, covering agent permissions and scope, protection of source code and sensitive data, validation of generated code and human accountability for changes; track adoption alongside delivery impact, quality, security and cost against an agreed baseline.
• Work closely with the Capability Leads to lead adoption of engineering standards across internal and third-party engineering teams, agreeing implementation priorities, coaching teams through adoption and reviewing evidence that standards are embedded in day-to-day delivery.
• Partner with the Architecture team to ensure engineering practices align with architectural principles, guardrails and technology strategy.
• Define engineering standards and create reference implementations, templates and reusable patterns that teams can adopt quickly; ongoing ownership and maintenance sit with the Capability Leads and their teams, not with the Principal Lead.
• Promote core engineering principles: small, incremental changes behind feature flags; trunk-based development with frequent, automated releases; test-first practices (TDD/BDD) and a balanced test pyramid including contract testing; peer code review standards; and secure-by-design delivery (e.g., threat modelling and automated security checks in the pipeline).
• Define and track engineering effectiveness measures, starting with the four DORA metrics (deployment frequency, lead time for changes, change failure rate and time to restore service), baselined per capability and reviewed regularly with the Capability Leads to evidence improvement over time.
• Mentor and coach Capability Leads, Technical Leads and engineers to raise technical capability across the organisation.
• Identify cross-capability technical debt, duplicated components and process bottlenecks, such as overlapping integrations between SAP, Domain Services and Storefront or manual release steps, and agree a prioritised remediation plan with the Capability Leads.
• Partner with the Data team to embed data quality, privacy-by-design and data contract standards into engineering practices, ensuring services and AI-assisted workflows handle data safely and consistently.
• Report progress, risks and outcomes regularly to the Engineering Manager.
• Agree a handover plan for each standard, reference implementation, reusable pattern and adoption measure, with named team owners and acceptance criteria, so that improvements are sustained beyond the contract period.

Skills & Experience

• Extensive experience as a Principal / Staff-level engineer or engineering lead, with breadth across enterprise commerce (SAP), cloud and DevOps, backend services, web storefront and native mobile (iOS and Android).
• Proven track record of defining and embedding engineering standards and best practice across multiple teams including 3rd party engineering teams.
• Hands-on experience introducing agentic development practices and AI-assisted development within the SDLC (e.g., GitHub Copilot, including agent mode), including governance, usage standards and measuring impact.
• Strong understanding of SDLC methodologies (Agile, DevOps, SRE, DevSecOps).
• Strong experience with CI/CD, infrastructure as code and automated testing strategies (TDD, BDD, test pyramid, contract testing).
• Strong experience implementing secure engineering controls (e.g., SAST, SCA, SBOM, OWASP).
• Experience with observability, monitoring and engineering metrics (e.g., DORA).
• Experience partnering closely with Architecture teams and third-party engineering partners to deliver shared standards.
• Working knowledge of data engineering practices, including data quality, privacy-by-design, data contracts between services and how data supports AI-assisted and agentic development.
• Experience working with agile tools such as Jira, Confluence and Azure DevOps / GitHub.
• Experience in retail or omnichannel environments.