tax disc or insurance? I assume that the situation i have described is not legal but please correct me if i am wrong.
Do people just take a chance on the journey home that they wont be caught ?
or do the police understand the situation and are happy to turn a blind eye if the auction papers are shown?

Legally you cant drive on the road without valid tax. If you already have Fully Comprehensive insurance for the car you are presently driving you can use the same insurance, providing you are the policy holder and also going to be driving the 'new' car home.

most auction houses will have a delivery service were by they will send a driver with trade plates to deliver the car to your home. This service is not cheap, they charge by the mile but it takes the worry out of driving a car with no legal documentation