What is Feature Flag? — UK Software Development Guide
Direct Answer
A feature flag (also called a feature toggle or feature switch) is a technique that allows software behaviour to be changed without deploying new code. Features can be turned on or off for specific users, groups, or environments — enabling: safe gradual rollouts, A/B testing, emergency kill switches, and canary deployments.
Feature-flag in the UK
Feature flags are particularly valuable for UK regulated software. For FCA operational resilience: a feature flag on a new payment flow enables instant rollback if unexpected problems emerge — meeting the FCA's requirement to demonstrate the ability to revert changes quickly. For NHS software: clinical safety (DCB0129) risk management benefits from gradual rollouts with monitoring. For UK GDPR: feature flags can be used to gate features that process personal data — enabling staged UK GDPR compliance rollout. Common UK tools: LaunchDarkly (enterprise), Unleash (open source, self-hostable for UK GDPR data residency).
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