The Health and Safety Executive (HSE) is the UK government body responsible for enforcing workplace health and safety legislation. For electrical work, the two primary pieces of legislation are the Health and Safety at Work Act 1974 (HSWA) and the Electricity at Work Regulations 1989 (EAWR).
HSE inspectors — also called inspectors of health and safety — have extensive legal powers to enter workplaces, examine equipment, take measurements, interview employees, require the production of documents, and take enforcement action. They focus on whether the duty holder (usually the employer or building owner) has taken all reasonably practicable steps to manage electrical safety.
For electricians, this means two things: first, your own working practices on site may be inspected; second, the electrical installations you maintain or certify may be examined as part of a wider workplace inspection. In both cases, competence and documentation are what the inspector is looking for.