AIUI, according to the local BCO that I had a chat with ...
self-closing doors are required on all 'habitable rooms'.
Their intention is to prevent the ingress of fire into
a habited room allowing the occupant to get out via the fire exit.


Its the other way round - the intention is to prevent fire within a
room spreading to the escape route to the outside. If you are in the
room with a fire then you know about it and escape, but if the fire is
in another room you want to be able to leave your room when the alarm
goes off, to a safe escape route not in flames. We have to do the same
with our chapel conversion. They are only looking after us!

cheers

Jacob