Everybody has missed a huge part of your question. The fire part, you can't simply start chopping locks into fire doors and expecting the integrity in the door to remain intact. You should buy intumescent packers to go around the lock and behind the strike plate to ensure full 30 or 60 mins protection. It is also advisable to take guidance from the door manufacturer, after all it was them who paid to test the door in the first place.

Either a nightlatch or a Euro sash/dead lock with an internal thumb turn would do in this instance. Either type would need to have the British Standard mark to ensure it will cope with the 30 minutes fire egress regulation. If fire regulations need to be met the cost should always be secondary and spending a few pounds more would ensure you get the product you need. There are to many to list but all manufacturers make a lock or locks that would be sufficient in this instance.
Cheers, Nat.

Yes a Euro profile dead lock or sash lock would be exactly what you need in that situation.
We fit this type of lock to HMO in Nottingham where guidelines are exactly the same as you raised - I would suggest you add a high security euro cylinder (thumb turn) with anti snap like a ABS or ultion.

Richard
LockSmart Locksmiths

You need a Din escape lock and cylinder.