Lofts are a long way above the ground, so you should consider fire escape routes. If you have a two-storey house, you will have to replace the existing doors around the whole staircase (except those to non-habitable rooms like bathrooms and cloakrooms) with fire- resisting doors, to make a fully-protected path to the ground-floor exit. The new room(s) in the loft also need to be provided with fire-resisting doors. Any glazing in the walls enclosing the stairs will also need to be replaced with fire-resisting glass.
If you have an open-plan layout, you must put in walls to separate your stairs from any rooms, and link them to an escape route to the outside.
Until April 2007, all doors to habitable rooms off the stairwell had to be provided with self-closers. You no longer need to do this, but everyone in the household will now have to be much more aware about the need to keep doors protecting your escape route closed, especially at night.
In a conventional two storey house loft conversion which i beleve yours is, there needs to be a protected route between the bedroom(s) door to the second floor level and the point where saftey is reached, normally the front door or access to the external parts.
Some building inspectors will accept automotic door closers fitted to all habitable room doors off this route, ie bedrooms, living rooms, plus the kitchen. Some, unfortunately will ask for fire rated doors to be installed. Any glazed doors will definately have to be replaced.