@dbr @Bainbridge - the mortgage requirements for "commercial" properties are much stricter than the residential ones so although some prices are attractive and change of use will be relatively straightforward to obtain, you will be asked for a larger personal input.
Case in point - I was looking to buy a 2 bed house for circa £450k in SE Zone2 .
I found a three storey office in Canada Water, facing the water. "Fixed" price £450k.
It was Ground Floor + 2 levels with a roof terrace which was being used as 3 "artist" studios but really people lived in there and did pay council tax. So a great space at 3x35sqm with 2 parking spaces.
The two offices on each side had successfully gained change of use to residential so you'd be pretty much guaranteed to get it as well.
And the way the cookie crumbled... I was asked to get 75% cash deposit for it and could only get a 25% mortgage. So I could not go for it, which is a shame.
Similar-ish situation happened for a commercial property on Dragonfly Place in Brockley SE4 - but that one was slightly different as the deeds prevented the change of use for 15 years from built IIRC.
Anyway, after this I ended up looking for a normal house...