In reply to Kemics:
I've had a couple of ex Royal Mail vans (cheap/cheerful/rubbish LDV Pilots), and currently have an ex-AA Renault Trafic. I wasn't brave/organised enough to get them at auction, but bought them from dealers who had. You pay a bit more that way but can at least have a test drive before you commit, get a bit of a warranty and wotnot. (Though what that is worth depends on the integrity of the dealer I suppose.)
I gather the state of the electrics with ex-AA vans can be pot luck. They take the light bar off the roof before the van goes to auction and apparently the care that goes into that job can vary a lot. I've spoken to people with similar vans who had to do a fair bit of work to make good the damage from a careless job. I got lucky in that it was neatly done leaving the rest of the extra gubbins the AA put in still there and working perfectly. (Some additional lights, sockets for jumpleads, etc.)
I wasn't so lucky to get one with a gearbox that gave up the ghost in the first year I had it. Expensive. Trafic gearboxes aren't the best anyway, this was probably down to ham-fisted towing rather than careless driving as such.
If you get a vehicle from a large fleet like British Gas or the AA, it will probably have a speed limiter fitted. It's usually fairly straightforward to get it removed, but doesn't always work apparently. (Mine was a software thing in the ECU, after checking that I didn't want the van speed-limited the dealer who sold me mine had it taken off by someone they use who specialises in remaps and such.)
My current van has a tailgate on the back, the previous one had barn doors. The tailgate is brilliant - instant shelter from the rain whilst changing etc. at the back of the van. Wouldn't be without it now.
Good luck!
Post edited at 11:56