My two bedroom flat has a fire alarm in the lobby and a detector, also in the lobby, for the centralised system for the whole block of flats. Is that sufficient? I have just had an electrician change my fuse box and he recommends "Supply and install new smoke alarms, comprising of 1 x smoke alarm in the lobby + 1 x smoke alarm in the living area + 1 x smoke alarm outside the kitchen + heat detector in the kitchen: £490". Is that necessary?