Ill have to get temp insurance either way because the car is currently not insured at all.
So yeh, looks like I've got 2 options, either mess around with taxing it myself and then SORNing it OR the 'leave cash with the seller while test driving the car' option.
Next question
Who does temp cover for modified cars? All the usual suspects say that the car cannot be modified, the car in question is modified.
I'm with Adrian Flux for my insurance on the derv with all mods declared so might call them up and see what they can do. Anybody else used Adrian Flux for this sort of thing?