Just insure the car and pick the monthly payment option, when you get your insurance cert ring them back up and insure yourself back on the micra or whatever car you have aswell, which means your only after paying a few quid if even for the cert because your insurance will go straight back down to the rate of the lower car and you'll have a cert to bring to the tax office etc, at the moment i have a 1.4 almera, and when I want to drive my 2 I just ring up and say im trying to sell it or someones coming to look at it, they dont charge me any extra at all, wearing a bit thin though

and you get a cert for the weekend etc if youve been stopped, happy days