Sector: Public Sector / Government Job Title: Senior Platform Engineer (Cross Domain Engineer) Type: Contractor Location: London (hybrid) Duration: 6 months initial Vetting: SC security clearance The Senior Platforms Engineer will provide advanced technical expertise across the organisation's Windows Server infrastructure and Cross Domain technology estate, ensuring the availability, security, resilience, and continual improvement of critical services operating within highly secure and classified environments. The role is responsible for the design, implementation, operation, support, and assurance of High Assurance Gateways (HAGs) and Cross Domain Solutions (CDS), enabling secure information exchange between UK Government classified networks. The post holder will support secure connectivity and controlled information transfer across OFFICIAL, SECRET, and TOP SECRET domains, ensuring compliance with NCSC guidance, UK Government security policies, accreditation requirements, and organisational risk tolerances. Working across infrastructure, networking, security, cryptography, and platform engineering teams, the Senior Platforms Engineer will design, implement, and maintain trusted gateway services that facilitate mission-critical collaboration while preserving the confidentiality, integrity, and availability of classified information. The role supports technologies including Cross Domain Gateways (iX), Data Diodes, Content Disarm and Reconstruction Platforms, Encryption Services, PKI Services, and Windows Server infrastructure. The contractor will be expected to operate autonomously, delivering high-quality technical outcomes aligned to sprint commitments, project objectives, security requirements, and operational service levels while supporting both strategic change initiatives and business-as-usual operations.
Essential Skills
- Significant experience as a Senior Platform Engineer, Infrastructure Engineer, Systems Engineer, or Cross Domain Engineer within complex enterprise, defence, government, or highly regulated environments.
- Proven experience designing, implementing, supporting, and troubleshooting Microsoft Windows Server infrastructure.
- Strong technical knowledge of: Windows Server 2016, 2019 and 2022 Active Directory Group Policy DNS DHCP Public Key Infrastructure (PKI) Certificate Services Identity and Authentication Services PowerShell VMware vSphere and Virtualisation Technologies Cross Domain Technologies
- Proven experience supporting, engineering, operating, or assuring High Assurance Gateways (HAGs), Cross Domain Solutions (CDS), or trusted information exchange platforms.
- Strong understanding of Cross Domain architectural patterns including: One-way information transfer (Data Diodes) Two-way controlled information exchange Multi-Level Security architectures Trusted Gateway Services Secure Replication Services Guard-based Information Exchange
- Experience implementing and managing information release policies, content validation controls, file sanitisation processes, malware inspection, and data transfer governance.
- Strong understanding of trust boundaries, security domains, data segregation, and secure information sharing principles.
- Experience supporting security accreditation, assurance activities, and evidence generation for classified systems and regulated environments.
- Strong understanding of cryptographic services, encryption technologies, PKI, certificate lifecycle management, and secure communications.
- Experience assessing and mitigating risks associated with classified information exchange and trusted data transfer mechanisms.
- Experience integrating Cross Domain technologies with enterprise infrastructure services including Active Directory, Identity Services, Security Monitoring platforms, SIEM tooling, and Windows infrastructure.
- Knowledge of secure information exchange requirements across Government, Defence, National Security, or Critical National Infrastructure environments.
Infrastructure & Engineering
- Advanced PowerShell scripting and automation experience.
- Strong understanding of Windows platform lifecycle management, system hardening, patch management, and vulnerability remediation.
- Experience troubleshooting complex infrastructure and platform issues at 3rd and 4th Line support levels.
- Demonstrable experience operating within Agile, DevOps, or product-aligned delivery teams.
- Experience using infrastructure monitoring, performance management, and operational tooling.
- Working knowledge of Jira, Confluence, and IT Service Management platforms.
- Good understanding of hybrid environments incorporating on-premise and cloud-hosted services.
- Familiarity with NCSC security guidance, Secure by Design principles, Zero Trust architectures, and UK Government security frameworks.
Desirable Skills
- Experience supporting products from vendors such as Everfox (Deep Secure/Garrison), Owl Cyber Defense, Opswat, Viasat CDS, Forcepoint, or similar Cross Domain technologies.