well phoned up and the reason they want a copy of the v5 is because on the quote it had selected that I hadn't bought the car yet. so don't think theres any thing dodgy. they do seem excessively picky though they also want 6 pictures including external interior and the engine bay! not that they will be able to tell as its so oily in there!
Did you double check the details passed from the comparison site to flux? They often "assume" certain details and it may be incorrect.
Comparison site is fine, but then double check the details with the actual insurers website when you click through before purchasing.