The Scottish Government has introduced legislation requiring smoke and
heat alarms to be interlinked:
https://www.gov.scot/publications/fi...cottish-homes/
As I see it, this can either be done by hard wiring or wireless
connection. Leaving aside cost and aesthetics for the moment, am I
right in thinking that wireless might be the safer option in case the
cables are damaged by the fire?

If I go for mains-powered units, could these be connected to the
lighting circuit or should there be a dedicated circuit?

I assume a separate link cable(s) is needed (not a signal via the
existing wiring). Should these be armoured to protect from fire :-)