Senior AI Software Developer

Mayfair IT Consultancy; Greater London; On-site; GBP 90,000 - 140,000; Full time

Job summary

Mayfair IT is seeking Senior AI Software Engineers, GenAI Engineers and LLM Engineers to build, deploy and support enterprise-scale AI-enabled applications for secure public sector environments.

Roles require strong foundations in Node.js and/or C#/.NET, with hands-on experience creating AI-powered systems using LLMs, RAG, and agentic AI patterns. Candidates should be familiar with GDS standards and GOV.UK Design System, and be prepared for government security requirements.

Qualifications

• Strong Node.js / JavaScript and/or C# /.NET development experience.
• Experience with Hapi.js and/or ASP.NET Core.
• Full Software Development Lifecycle (SDLC) experience.
• REST APIs and Microservices.
• Cloud-native application development.
• Distributed Systems.
• Event-Driven Architectures.
• Automated Testing and TDD.
• Docker and Containerisation.
• MongoDB and/or PostgreSQL.
• GDS service delivery experience.
• GOV.UK Design System experience.
• Agile delivery experience.

Responsibilities

• Design, develop, deploy and support secure production applications.
• Build services using Node.js, JavaScript, Hapi, C#/.NET and cloud-native technologies.
• Develop citizen-facing services aligned with GDS standards and the GOV.UK Design System.
• Develop APIs, integrations, workflows, microservices and distributed systems.
• Build and deploy AI-enabled applications using LLMs and enterprise data.
• Implement RAG, prompt engineering and agent orchestration patterns.
• Build agentic workflows and multi-agent systems.
• Create AI evaluation frameworks, deterministic testing strategies, evals and rubrics.
• Use GitHub Copilot, Claude Code and OpenAI Codex throughout the SDLC.
• Create and maintain repository instructions, reusable prompts, skills and agent configurations.
• Deploy and support applications running on Azure and AWS.
• Contribute to technical leadership, architecture and engineering best practices.
• Support monitoring, reliability, testing, operational readiness and incident management activities.

Skills

Node.js/JavaScript

C#/.NET

Hapi.js

ASP.NET Core

REST APIs

Microservices

Cloud-native

Docker

Agentic AI

Tools

Azure

AWS

Terraform

Kubernetes

GitHub Actions

Job description

Overview

Mayfair IT is supporting a major UK Government AI and Digital Transformation programme. We are seeking experienced Senior AI Software Engineers, GenAI Engineers and LLM Engineers to build, deploy and support enterprise-scale software and AI-enabled applications across secure public sector environments. This role combines traditional software engineering, cloud-native delivery and modern AI engineering.

Successful candidates will leverage AI-assisted development throughout the Software Development Lifecycle (SDLC) while delivering secure, scalable and maintainable production systems. The ideal candidate will possess strong software engineering foundations, ideally in Node.js and/or C#/.NET, alongside practical experience building AI-enabled applications using Large Language Models (LLMs), Retrieval-Augmented Generation (RAG), Agentic AI and AI-assisted engineering practices.

What You’ll Be Building

• Citizen-facing GOV.UK services using GDS standards and the GOV.UK Design System.

• AI-enabled applications integrating enterprise data, APIs and business workflows.

• Retrieval-Augmented Generation (RAG) solutions and knowledge retrieval platforms.

• Agentic AI applications and multi-agent workflows.

• AI-powered search and automation platforms.

• Internal AI Engineering Platforms, reusable templates and developer enablement tooling.

• Cloud-native applications deployed on Azure and AWS.

Examples of You Will Be Building

• Agentic AI applications that process documents, validate information and update enterprise systems through controlled API and tool interactions.

• AI Engineering Platforms providing reusable templates, repository instructions and coding-agent workflows.

• GDS-compliant applications that collect information, execute workflows, call APIs and generate business outcomes.

• RAG-enabled solutions integrating enterprise knowledge repositories, document stores and databases.

• AI-enabled applications powered by Azure OpenAI, Microsoft Foundry and AWS Bedrock services.

Key Responsibilities

• Design, develop, deploy and support secure production applications.

• Build services using Node.js, JavaScript, Hapi, C#/.NET and cloud-native technologies.

• Develop citizen-facing services aligned with GDS standards and the GOV.UK Design System.

• Develop APIs, integrations, workflows, microservices and distributed systems.

• Build and deploy AI-enabled applications using LLMs and enterprise data.

• Implement RAG, prompt engineering and agent orchestration patterns.

• Build agentic workflows and multi-agent systems.

• Create AI evaluation frameworks, deterministic testing strategies, evals and rubrics.

• Use GitHub Copilot, Claude Code and OpenAI Codex throughout the SDLC.

• Create and maintain repository instructions, reusable prompts, skills and agent configurations.

• Deploy and support applications running on Azure and AWS.

• Contribute to technical leadership, architecture and engineering best practices.

• Support monitoring, reliability, testing, operational readiness and incident management activities.

Essential Skills & Experience Software Engineering

• Strong Node.js / JavaScript and/or C# /.NET development experience.

• Experience with Hapi.js and/or ASP.NET Core.

• Full Software Development Lifecycle (SDLC) experience.

• REST APIs and Microservices.

• Cloud-native application development.

• Distributed Systems.

• Event-Driven Architectures.

• Automated Testing and Test-Driven Development (TDD).

• Docker and Containerisation.

• MongoDB and/or PostgreSQL.

• Production support and operational ownership.

• GDS service delivery experience.

• GOV.UK Design System experience.

• Agile delivery experience.

AI & GenAI

• LLM application development.

• Retrieval-Augmented Generation (RAG).

• Prompt Engineering.

• AI Agents and Agentic Workflows.

• Agent Orchestration.

• Multi-Agent Systems.

• Tool Calling and Structured Outputs.

• AI-assisted development practices.

• GitHub Copilot, Claude and/or OpenAI Codex.

• AI Evaluation Frameworks.

• Evals and Rubrics.

• Deterministic Testing.

• MCP Servers.

• Production AI Monitoring.

• AI Testing, Validation and Observability.

• Production AI Deployments.

Cloud & DevOps

• Azure and/or AWS.

• Terraform and/or Bicep.

• Infrastructure as Code.

• GitHub Actions or Azure DevOps.

• CI/CD Pipelines.

• Kubernetes (Desirable).

• Azure OpenAI.

• Azure AI Search.

• Azure AI Document Intelligence.

• Microsoft Foundry.

• AWS Bedrock.

• AWS Bedrock AgentCore.

Reliability & Security

• OpenTelemetry.

• Azure Monitor, Application Insights and/or CloudWatch.

• Identity-first security principles.

• Least Privilege Access Controls.

• Threat Modelling.

• Prompt Injection Protection.

• Data Leakage Prevention.

• Secure Secrets Management.

• Operational Readiness Reviews.

• OWASP Security Standards.

• Container, Dependency and Vulnerability Scanning.

• Application Monitoring and Observability.

Highly Desirable

• Public Sector experience.

• Central Government programme experience.

• Active SC Clearance.

• Agentic AI and Multi-Agent Systems.

• SharePoint integrations.

• Semantic Search and Vector Search.

• AI Search and Knowledge Management platforms.

• AI Governance and Responsible AI.

• Domain Driven Design (DDD).

• CQRS.

• Event Sourcing.

• Conversational AI.

• Cloud-native architectures.

• Public Sector Digital Transformation programmes.

Clearance Requirement

Candidates must hold Active SC Clearance.

Unfortunately, SC-Eligible, previously held, expired or lapsed clearances cannot be considered.