Lots of good suggestions already on who to approach. I would add one further comment. Dealers' valuations are often given for insurance purposes and, as such, are 'optmistic' (to allow for a cherished pride and joy to be replaced at retail prices). Whilst I am not suggesting you mislead HMRC, you need a realistic valuation along the lines of "what would you offer me right now to take the car away?" Which will of course be significantly lower than the normal insurance-type valuation. Apologies if this is self-evident & I'm not trying to patronise.
