John Rumm wrote:

Again don't know, why not phone em and ask?

The above advice is really crucial: assuming you're doing this job
properly and legally (which you should do, and it sounds like you are!)
you'll need to have the BCO out to inspect it. He will know exactly
how he wants the job doing, and it's all very well to do the necessary
work according to your interpretation of the Building Regs documents or
what other folk have advised here, but at the End of the Day it has to
satisfy the BCO or he'll have you ripping it all out and starting again.
There might even be other aspects of the project which will attract
their attention other than fire regs which you haven't considered.

So contact the Building Regs dept first and ask them exactly what they
want you to do in order to comply; they're usually very happy to help
IME. Your best bet is probably to wander into the council offices with
a sketched plan of the flat layouts etc and have a chat with the duty
BCO. If you're lucky they might even come round for a looksee before you
even start work.

David