no where is the answer... Not a single response advertisied privately. I suspect private sales over £20k are rare for a run of the mill car, with buyers probably favouring dealers for piece of mind and finance.
Car went to WBAC who offered more than any other buying service.
With a recent 20k budget, I was looking on Autotrader. Would happily have brought from a private seller, but found the best price/car combo from a dealer.