Donald Trump was scheduled to take his first international trip since presumptively clinching the Republic an presidential nomination, jumping out of the US political frying pan and into the "Brexit" fire by arriving in Scotland on Friday.

The New York celebrity billionaire will attend the ceremonial re-opening of his Trump Turn berry golf course on the very day that the British will wake to learn whether they have voted to remain in the European Union or backed the historic move to defect from the 28-member bloc.

With the intense campaign in Britain coming down to the wire, and British Prime Minister David Cameron invoking wartime spirit to call on citizens not to "walk away" from European democracy, Trump repeated his position that the British should leave the EU.