Partially Boarded Loft Conversion

[UKLEEJ]

Hi, I'd be really grateful if someone could help me on this matter.

I bought my 2 bed terraced house just over 3 years ago. The paticuars from the estate agents stated the house included a partially boarded loft conversion. I later found out that it was not listed as a third bedroom as the previous owners had not applied for planning permission some 8 years earlier although it was used as a bedroom - all be it a very tiny one. We are now planning to use this space as an office and use a built-in ladder to gain access.

I was wondering, when we come to sell our house in the near future how I would go about listing it as a third bedroom or office space as opposed to a partial loft conversion. For example, would i have to put in a stair case, apply to the council for permission or pay out to have it extended as both sides are sloping roofs?

Any help/advice would be very much appreciated.

Thanks