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The building control officers, and your architect, will be referring to BS5839-6 when looking at the specification, the design guidance will be in there.
On reflection they're probably asking for a Grade D (mains) LD1 system. This is common enough for small loft conversions in lieu of creating a protected stairwell using fire doors. That's alarms in all circulation spaces and any rooms where a fire might start, so basically everything except your bathroom.
Probably quite difficult to answer. I thought fire doors were compulsory and I've seen all sorts of stupid temporary solutions to building regs requirements. I got pulled on not using fire door stop on a project once, sadly the regs are partially based on examination of fatal failures though.