Dunno if anyone spotted this, but I only just found it.
If you buy or sell a car on ebay, Norwich Union will give you 7days fully comprehensive cover on the car.
Ideal for when you go to pick up that impulse bought ebay motor, giving you a chance to sort out insurance later.
Also useful for getting the car taxed if it wasn't already.
Check out the details:
http://pages.ebay.co.uk/motors/services/7dayinsurance/I know it would have been useful for me, the couple of times I've bought to sold cars and had to add them to my policy.