Stanner is quite correct.
Though I cannot quote the HMRC communications directly due to its marking, here is the bottom line and why. This applies to a NEW vehicle import to the UK from the EU and I am absolutely content it is the Gospel truth.
1) The German (say) dealer is entirely in its prerogative to charge German VAT. They are liable if it is subsequently shown that one of its customers evaded VAT. However, they WILL refund the VAT when given an original receipt by the UK's HMRC showing UK VAT paid.
2) HMRC will not accept prepayment of VAT on the basis of the invoice. This is because they cannot levy VAT on a vehicle that has not yet arrived in the UK, as they have no legal right to demand or collect the tax on a vehicle that is not physically here.
Thus, as HMRC concede, there is no way for the buyer to be in control of avoiding paying, albeit temporarily, two lots of VAT.
On the upside, I have got HMRC to apologise for the wrong (albeit consistently so) advice given by 3 of their staff on 3 separate occasions, and there will be training to remedy this.
Also, I am now sitting on a load of Euros back from the dealer as a refund of the VAT, and watching the exchange rate with amusement. My only dilemma is whether to convert them to sterling on the eve of the Scotland referendum, or if I think a Yes vote will win, hold onto them for more gains as sterling tanks.
Dave