Sorry, but have to disagree on this. Ex-BCO and plenty of experience with dodgy loft conversions!
The important point is whether the room is habitable or not. This is not determined by the means of access to it. It is a question of judgement, but if you have boarded floor and ceilings, fully insulated, power, light, etc, it would be classed as a habitable room. B Regs would then require safe access/egress from it, ie full blown loft conversion.
If you need to make any structural alterations, eg if it's a trussed rafter roof, you would need B Regs approval, irrespective of whether it is a "loft conversion" or not.
Of course, you could take the risk and just do it, because the local authority are unlikely to find out about it, but that would probably invalidate your house insurance. You may also come unstuck when you come to sell. I don't think it's worth it really.
The important point is whether the room is habitable or not. This is not determined by the means of access to it. It is a question of judgement, but if you have boarded floor and ceilings, fully insulated, power, light, etc, it would be classed as a habitable room. B Regs would then require safe access/egress from it, ie full blown loft conversion.
If you need to make any structural alterations, eg if it's a trussed rafter roof, you would need B Regs approval, irrespective of whether it is a "loft conversion" or not.
Of course, you could take the risk and just do it, because the local authority are unlikely to find out about it, but that would probably invalidate your house insurance. You may also come unstuck when you come to sell. I don't think it's worth it really.