No, you cannot just buy, pay and drive it away. From the BCA website:
“Remember that it’s an offence to drive a vehicle on the road without valid insurance, a current Vehicle Excise Licence and MOT certificate (if applicable), so you need to make suitable arrangements.”
As part of the “suitable arrangements” under the “Continuous Insurance” regulations all vehicles must now be insured in their own right before being kept or driven on the road. The full details are here:
http://www.mib.org.uk/Motor+Insurance+Database/en/Continuous+Insurance+Enforcement/default.htm
But to save you looking it up, the first paragraph says this: “As part of Continuous Insurance Enforcement (CIE), it is now a legal requirement for registered vehicle keepers to insure their vehicle(s) at all times.”
On your own policy you may be insured to drive cars not belonging to you (and even this is dodgy because you may have difficulty convincing the police that a car you had just bought and paid for is not yours) . But the car must have a policy which covers it in its own right and it must be recorded on the Motor Insurers’ Database. If not you risk having the car impounded as well as being prosecuted for No Insurance (minimum six penalty points). You are most unlikely to be able to buy a traders’ policy as (I assume) you are not a trader.
So unless the auction house has some sort of arrangement to temporarily provide cover for cars that they sell (as some motor traders do) you will have to arrange cover.