Two electric supplies

[ban-all-sheds]

Yes, but the supplier can still insist on only providing a single supply if from his POV it's a single installation.

Hence my suggested questions above - once JezR has established what sort of cables can run between the two halves without the supplier getting their panties in a knot he can (almost certainly) find a fire alarm system that doesn't bother them.

 

[OwainDIYer]

It's absolutely normal to have fire alarms across multiple addresses in blocks of flats with/without shops on the ground floor. In buildings on a corner, the flat's postal address might not be on the same street as the shop, and anyway the flats might have a completely separate incomer(s).

I'm not sure but I think the fire alarm circuits should be SELV if that helps?