Private reg transfer & selling a car ?

[philip600]

Hi, my Son has recently bought another car as a replacement to his existing one. He has left a deposit on the new one on 21/2 & the dealer sent off paperwork that day to transfer my Sons private plate onto new car. In the meantime he has sold his other car but told the buyer he couldn't collect the car until the plate transfer has completed. Now he is picking up his new one tomorrow albeit on the original plate but the buyer of his old car is wanting to collect it asap. The buyer has offered to sign a receipt that says the registration number is not part of the sale but I'm a bit worried about letting it go until the plate transfer is complete, am I right to be concerned ?

Phil.