Boris Johnson has contacted millionaire donors to the Brexit campaign to express his fury over HM Revenue and Customs’s decision to charge inheritance tax on donations to the campaign to leave the European.

Demands running into millions of pounds have been sent to several major donors to the campaign to leave the EU and at least one major Remain supporter.

Yesterday Stuart Wheeler, a City spread betting tycoon, told The Telegraph that he had just paid £250,000 on his £1million-plus donation after being threatened with interest bills.

The Daily Telegraph disclosed last weekend that demands running into millions of pounds have been sent to at least three major donors to the campaign to leave the EU - Peter Cruddas, a City financier, Lord Edmiston, a Midlands entrepreneur, and Arron Banks, an insurance tycoon, and a single major Remain supporter, David Harding.

In the letters the tax authorities had seized upon a relatively obscure area of inheritance tax laws which forces people to pay the 20 per cent tax upfront on large "gifts".

The demands will disproportionately hit Leave supporting donors because the various 'out' campaigns were financed by entrepreneurs rather than mainstream publicly listed companies which tended to back Remain.