Who enforces the Fire Safety order in the UK?

The local fire and rescue authority (the fire and rescue service) will enforce the Fire Safety Order in most premises.

The exceptions are:
• Crown-occupied/owned premises where Crown fire inspectors will enforce;
• premises within armed forces establishments where the defence fire service will enforce; and
• certain specialist premises including construction sites, ships (under repair or construction) and nuclear installations, where the Health and Safety Executive (HSE) or local authority will enforce.

What is more difficult is evidencing an enforcement case against the fire alarm engineer?