SDS supply all the ironmongery you would need to make the building regs people and you happy with your loft extension. Talk to one of our people on 0207 228 1185 or ask in our shop on Northcote Road.
Type in fire door in the search field on
http://www.sdslondon.co.uk this will give you the door closers and other things you will need.
Signage, smoke alarms, fire seals, intumescent fire grilles, fire blocks etc.
A good website is
http://www.means-of-escape.com/ which has fire safety guides and other advice.
Good luck
Tracy