Might be worth anyone's time getting a quote from Footman James. They are by far the cheapest I can find.
For a 60s Volvo with modified suspension, 140bhp 2.3ltr swap, £250 separate stereo cover, unlimited mileage, Europe-wide breakdown cover, £50 excess (I think, it was without the engine swap), tp on other vehicles, they quoted just under £200 fully comp. It was about £50 less with the same spec minus the engine swap.
I'm early 30s with no no-claims. They don't let you build up any no claims with them, but with a premium that low I'm laughing too hard to care. I had a quote from Adrian Flux for about £500 fully comp on the stock wagon. Had one from Brentacre for just under £1300 for the wagon+engine swap. There were more but you get the idea.