1. Even if the loft room is not being marketed as an extra bedroom does this still require building regs?
Yes. The loft has been converted into a habitable room so it does require building regulations approval
2.Am I correct in thinking that as the loft has been converted into useable /habitable space regardless of the specific intentions of its use; storage or bedroom this will need building regs approval?
Yes you are correct. Any conversion work that converts the empty roof space into a habitable room requires building regulations approval even if the room is subsequently used for storage. Before buying the house insist on seeing the final completion certificate that should have been issued by the building control office. If this cannot be produced and you go through with the purchase there could well be issues further down the road. Consider asking your solicitor for advice.
3. Would all 6 doors leading from the main upstairs landing need to be fire doors or solely the door giving direct access to the loft (the staircase to the loft is fully boarded)?
The building regulations state that all the doors in the house along the protected escape route have to be capable of resisting fire for at least 20 minutes. It is important to remember that partition walls along the escape corridor must also be fire resistant and that the protected stairway should have 30 minutes fire resistance.