How can I insure a vehicle I am restoring but do not own so that I can drive it to the MOT station?

My son owns and is the keeper of a 1969 mini. We have been restoring it ready for when he can learn to drive (5 months time - Sep 2010). I need to insure it so I can get an MOT and tax to complete the restoration. I cannot find anyone who will insure a vehicle that is:

• 1) not owned/registered in my name and
• 2) is of 41 year vintage.

Other than registering it to me for 6 months thereby decreasing the value, how do I get it insured? Would I be covered via the comprehensive cover on my own car to drive it legally to the MOT station or if I get stopped by the police, could they seize/crush the vehicle? All the temporary cover companies I've tried don't touch anything older than January 1970.