Why Zero Trust for UK Government
Traditional network security operated on a simple premise: build a strong perimeter, and trust everything inside it. This castle-and-moat approach has become fundamentally inadequate. Cloud services, SaaS applications, and flexible working mean the network perimeter has effectively dissolved.
The NCSC's Zero Trust Architecture guidance addresses this reality. As the NCSC states: "In a zero trust architecture, inherent trust is removed from the network. Just because you're connected to a network doesn't mean you should be able to access everything on that network."
For UK government and public sector organisations, this represents a fundamental shift. The Home Office Engineering Guidance now mandates zero trust principles, requiring access policies based on least privilege and the assumption that all requests are potentially hostile.
The 8 NCSC Zero Trust Principles
The NCSC provides eight principles to guide zero trust implementation in enterprise environments:
Principle 1: Know Your Architecture
Before implementing zero trust, you must identify all users, devices, services, and data within your architecture. This includes understanding where sensitive data resides, how it flows, and who legitimately needs access. Without this foundation, you cannot develop effective access policies.
Principle 2: Know Your User, Service, and Device Identities
Strong identity is the cornerstone of zero trust. Every user, service account, and device must have a verifiable identity. This requires robust identity management systems, ideally integrated with Azure AD or equivalent identity providers that support modern authentication protocols.
Principle 3: Assess User Behaviour and Service Health
Zero trust extends beyond initial authentication. Continuous assessment of user behaviour and device health informs access decisions. Anomalous behaviour patterns or compromised device posture should trigger additional verification or access restrictions.
Principle 4: Use Policies to Authorise Requests
Every access request must be evaluated against explicit policies. These policies consider multiple signals: user identity, device health, location, time, requested resource sensitivity, and behavioural patterns. Policy engines become the central decision point for all access.
Principle 5: Authenticate and Authorise Everywhere
Authentication and authorisation must occur for every request, not just at the network edge. This applies to internal service-to-service communications as much as external user access. Mutual TLS, service mesh architectures, and API gateways enforce this principle.
Principle 6: Focus Your Monitoring
With authentication everywhere, you gain unprecedented visibility into access patterns. Focus monitoring on detecting anomalies, policy violations, and potential compromises. Security information and event management (SIEM) systems must aggregate and analyse these signals effectively.
Principle 7: Don't Trust Any Network
This is perhaps the most fundamental principle. No network—including your own corporate network—should be inherently trusted. All traffic should be encrypted, and access decisions should never rely solely on network location.
Principle 8: Choose Services Designed for Zero Trust
When selecting services, prioritise those with native zero trust capabilities. Cloud services from Azure, AWS, and Google Cloud increasingly support zero trust patterns. Legacy systems may require additional security layers or should be prioritised for modernisation.
Implementation Roadmap
Phase 1: Discovery and Assessment
Map all users, devices, applications, and data flows. Classify data sensitivity and identify critical assets. Assess current identity and access management capabilities against zero trust requirements.
Phase 2: Identity Foundation
Implement strong identity management with multi-factor authentication. Establish device identity and health assessment capabilities. Deploy privileged access management for administrative accounts.
Phase 3: Network Microsegmentation
Segment networks based on data sensitivity and access requirements. Implement software-defined networking to enforce micro-perimeters. Deploy network detection and response capabilities.
Phase 4: Application Security
Protect applications with secure access service edge (SASE) or zero trust network access (ZTNA) solutions. Implement API security and service mesh for microservices architectures.
Phase 5: Continuous Improvement
Establish security operations capabilities to monitor and respond to threats. Implement continuous compliance monitoring. Regularly review and refine access policies based on operational experience.
Technology Components
A zero trust architecture typically comprises several key technology components:
Identity Provider – Azure AD, Okta, or equivalent for user and device identity
Policy Engine – Central decision point evaluating access requests against policies
Policy Enforcement Points – Gateways and proxies enforcing policy decisions
SIEM/SOAR – Security monitoring, analytics, and automated response
Endpoint Detection and Response – Device health and threat detection
Network Detection and Response – Traffic analysis and anomaly detection
Data Loss Prevention – Protecting sensitive data from exfiltration
Government Supplier Requirements
Organisations supplying services to UK government must increasingly demonstrate zero trust capabilities. This is particularly relevant for suppliers handling OFFICIAL-SENSITIVE or higher classifications.
Key requirements include alignment with NCSC zero trust principles, Cyber Essentials Plus certification as a baseline, evidence of continuous monitoring and incident response, and documented access policies with regular reviews.
The NCSC Cloud Security Principles complement zero trust guidance, and suppliers should demonstrate compliance with both frameworks.
Migration Strategies
Most organisations cannot implement zero trust overnight. The NCSC recommends a phased approach:
Start with High-Value Assets
Identify your crown jewels—the most sensitive data and critical systems—and implement zero trust protections there first. This delivers maximum security benefit with focused effort.
Use Cloud Transitions as Opportunities
When migrating workloads to cloud platforms, implement zero trust from the outset. It's easier to build zero trust into new deployments than retrofit legacy systems.
Address Quick Wins
Some zero trust capabilities can be deployed rapidly: enforcing MFA everywhere, implementing conditional access policies, and encrypting all network traffic. These quick wins build momentum and demonstrate value.
Plan for Legacy Systems
Some legacy systems cannot support zero trust natively. Strategies include isolating them behind zero trust proxies, implementing additional monitoring, or prioritising them for replacement.
The NCSC's GitHub repository provides additional resources and guidance for organisations implementing zero trust architecture.
