Surely even if the HMRC muggers do tax the allowances we 'just' need to keep the receipts and stick them on a tax return at the end of the year.
For me this would actually result in me paying less tax, not more, due to our allowance rate and the cost of most of our layovers.
I know its a ballache, but burying these morons in paperwork is one way to get back at them!