Ah right - well Chas does have it pretty much spot on there.
However, you can still get insurance without the reg - you;d need to go via an import specialist (like Adrian Flux). The previous insurer I worked for had a lot of work off them - we had quite a few people in your position.
Obvously the policyholder's couldn't drive their cars, but had trailored them home and obviously wanted the cars insured then - they usually allow the insurance on the VIN until you get the reg dox from the DVLA.
Same actually applies to the MOT (If I remember correctly - someone will set me straight), you don't need the reg to get it MOT'd, but again once the reg is known, I think you;d have to get a duplicate MOT with the reg on it.
But as for driving it, it's a no-no