If the room is habitable (i.e. a bedroom or living room) then there are lots of regulations applicable. Most importantly Approved Document B of the Building Regulations : Fire Safety. Contravention of this regulation is a criminal offence and punishable by a prison term of which ignorance is no defence. A suitable means of escape in the event of a fire should be provided for all occupants of the building from all floors without passing through a room. Therefore, a protected corridor needs to be provided from the attic and all floors below right down to the exit. This is usually acheived by fire doors and walls around the stairs.
The second factor that needs to be addressed is the structural performance of the attic floor and roof structure. Light domestic storage is one thing, you and eight of your fat mates getting excited over Scalextric is another loading scenario all together.
I strongly suggest that you get a local structural engineer to look into these aspects to ensure that your attic is suitable for the purpose you intend to use it for. An architectural consultant should also be consulted with regard to the fire regulations.
If you think that all this isn't worth it, think again. People die everyday in housefires in well designed houses that comply with the building regulations. You do not stand a chance should the unthinkable happen in a house that doesn't comply.