Can anyone help? I've bought a car without any documents and I want to tax it.
Official line is I can't until I get a V5 from DVLA.
But I know for definite that some people do get round this. Some car dealers do it somehow but I don't know how.

I believe the car is MOT'd but I can't find out, there is no V5 or new keepers supplement. The car is still registered in the old owners name;so I can't do it online or at a DVLA office.

I misread the Direct.gov website and I thought that with a V62 form I could tax it; but I don't beleive I can.

Does anyone know how?

I think you need to send off the V62 and wait unfortunately.
As you say, you can tax a car at a DVLA office immediately with a V62 if you are already the registered keeper but don't have a V5 yet.
Could you get the previous keeper to do it?