Place we're looking at has had the conversion done, undoing it would make a nice garage with the boarded walls and ceiling, just needs the floor tiling to finish it off.
Thanks for the replies. No habitable space above the garage. I was expecting a fire door would be a requirement. So is it necessary to involve planning or building regs or just for a builder to self certificate the work ?
Sadly the garage in question turned out to have some historic subsidence damage, though it doesn't seem to have got worse in over 10 years and I would have sorted it out after purchase I think it casts a shadow over the whole property.