When does HMRC advise a professional valuation?
HMRC's notes say you do not have to pay for one for an ordinary second-hand car you can estimate from public data. They advise a professional valuation if an item may be worth more than £1,500, or you are not sure.
HMRC does not name a damaged, modified, imported or classic car. In our view public data describes those cars poorly, so an estimate is hardest to support there. See who can value a car for probate.