Tonight at The Ritz London, there will be a lavish drinks party in honour of Nigel Farage.

Around 100 of his closest friends and supporters have been invited to the five-star hotel for a thank-you celebration for his role in the referendum, and an acknowledgement of the 25 years of his life he has devoted to getting Britain out of the EU.

And had Donald Trump lost the US presidential election, he would have been among the guests.

For a few weeks ago, when the polls suggested Trump would fail to be elected to the White House, he told Farage that he would attend the party 'win or lose'.

When the polls suggested Trump would fail to be elected to the White House, he told Farage that he would attend the party in his honour tonight 'win or lose' - but a change in result meant a change in tactic

But after having won, he realised that he couldn't spare the time coming to London – and decided to do the next best thing: invite Farage to Trump Tower in New York for a meeting, making the interim Ukip leader the first major foreign politician he received.

With this dramatic gesture, Trump didn't so much as upset the diplomatic apple cart as kick it over.

More to the point, he was deliberately ignoring protocol and enjoyed the ensuing spectacle of stuffy diplomatic noses put out of joint.

Trump's characteristic refusal to play by the traditional rules is also behind his cheeky suggestion that Farage should be Britain's ambassador to the US.

The idea is a very painful message for Downing Street officials and the Foreign Office about how the stakes in the game of diplomacy between London and a Trump administration in Washington have been raised.

Trump was fully aware that his tweet – said to be a little piece of 'friendly' advice – would cause a political storm in the UK

Trump was fully aware that his tweet – said to be a little piece of 'friendly' advice – would cause a political storm in the UK.

It brutally emphasised his position of strength. For he realised that Prime Minister Theresa May would have no choice but to reject his advice (for a host of political reasons) and this would put them on collision course.

I'm told that his 'Farage for ambassador' suggestion was meticulously 'war-gamed' by his advisers.

In other words, the ploy was analysed at length and the note only sent after consideration of all possible tactics and the likely response.

Of course, Trump's team never expected that Mrs May would welcome the suggestion and jettison the current UK ambassador to Washington, Sir Kim Darroch (a career diplomat with special interests in national security issues and the EU) to make way for a man who has caused the Tory Party so many problems.

They were simply trying to test Mrs May and sending a typically blunt message about how Trump intends to operate as president.

Trump's team never expected that Mrs May would welcome the suggestion and jettison the current UK ambassador to Washington, Sir Kim Darroch to make way for a man who has caused the Tory Party so many problems

As a result, Downing St can be in no doubt that when it comes to his dealings with Britain, as with everything else, 'The Donald' will not play by the rules.

In time, he may inevitably be more restrained, but for now, at least, he intends to do things his way.

As someone based in Britain who has been in daily contact with his team since his election told me: 'Fellow world leaders and diplomats had better get used to such behaviour.

'If they want to deal with him, they have to realise that Trump doesn't have any truck with diplomatic niceties.

'He thinks all that stuff is part of the Establishment 'swamp' which he has vowed to drain.'

Meanwhile, Trump's very close relationship with Farage is going to pose a major problem for Mrs May.

Already, the photo of the Ukip leader and Trump grinning together beside the gold-plated doors of the latter's apartment in Trump Tower must have been galling to the Prime Minister.

Trump's very close relationship with Farage is going to pose a major problem for Theresa May

What's more, Trump's advisers are taking daily advice from Farage, who ten days ago mischievously said Mrs May ought to meet Trump – particularly after her team had been 'quite rude' about him and that there were 'fences to be mended'. For her part, Mrs May undoubtedly hopes that the issue over the choice of UK ambassador to the US will blow over.

Downing Street will agree the view of a former holder of that post, Sir Christopher Meyer, who said yesterday that our ambassador 'exists to defend UK interests in US, not US interests in UK' and that we 'can't have foreign presidents deciding who our ambassador should be.'

But with Trump calling the shots with his incendiary suggestion, urging the British Government to give his buddy a key job, Mrs May has been put in a quandary.

Behind all this is the fact that the Trump camp hold in disdain our current ambassador and do not want do business with him.

Privately, they describe Sir Kim Darroch in graphically rude terms.

This is not a good basis on which the Foreign Office to proceed as it tries to strike a new, favourable, trade deal for Britain with Washington post-Brexit.

This said, Trump is very keen that Britain makes a success of life outside the EU. Not only does he love the UK, he's also compared his own 'Make America Great Again' project to Brexit.

This means that his belief in our two countries sharing similar ideals gives him an emotional stake in Britain's future outside the European Union.

As a result, having an Anglophile in the White House should be good news for Britain – certainly better than was the case with Barack Obama who warned that the UK would be at the 'back of the queue' in any trade deal with the US if we quit the EU.

So, Mrs May ought to take advantage of Farage's hotline to the Oval Office. She must try to defuse Trump's animus against Sir Kim Darroch.

One way would be to find a suitable role for Farage.

Not only does Trump love the UK, he's also compared his own 'Make America Great Again' project to Brexit

While making him our ambassador is clearly out of the question, an elegant solution might be to appoint him as a special envoy or give him a role with one of the ministerial teams planning Brexit.

If that happens, for the first time in his political career, he would be 'inside the tent' rather than outside it making life awkward for the government of the day.

Giving him a long overdue peerage or knighthood – as I expect will happen in the New Year's Honour List – would reinforce his status and smooth the way.

Of course, Mrs May would absolutely hate doing this – and it would also attract a huge deal of opprobrium from Farage's many enemies.

Of course, Nigel Farage is a divisive character. But like or loathe him, as is the case with Donald Trump, he gets things done.