THERESA May has been warned by Nick Clegg, the former Deputy Prime Minister, not to be drawn into an “axis of aggressive Nationalism” as she prepares to meet Donald Trump in Washington later this week.

The Prime Minister is due to attend and speak at an informal Republican Party event in Philadelphia on Thursday before travelling to Washington DC for a bilateral with the new US President. Details, which could include a joint press conference at the White House, are still being worked on.

But speaking ahead of Mrs May’s visit, Mr Clegg warned that her approach to Brexit risked making her the "unwitting tool" of aggressive nationalists seeking to tear the European Union apart.

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At a conference in Brussels today, the former Liberal Democrat leader will label Mr Trump as part of an "axis of aggressive Nationalism," stretching from the White House to the Kremlin and taking in hardline Brexiteers in the UK and populist parties in countries across Europe.

Mr Clegg will urge the PM to put Britain's interests first at the White House and not to be drawn into the President's "Nationalist tactics to undermine the EU".

Party aides suggested he would accuse Mr Trump of "effectively colluding" with Russian leader Vladimir Putin to undermine the security and prosperity of Europe.

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"Theresa May's approach to Brexit is not only contrary to Britain's national interest, it also runs the risk that the Brexit negotiations unwittingly become the means by which the forces of aggressive Nationalism seek to unpick the EU itself,” the former DPM is expected to tell the E!Sharp conference.

"This has long been the stated ambition of the most hardline Brexiteers, and was repeated at the meeting of populist parties held in Koblenz this weekend.

"My message to Theresa May is clear: as you travel to Washington this week, beware the dangers of becoming an unwitting tool for the isolationism of Trump, Putin and Nationalists across Europe.

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"Her vision for a hard Brexit will pull us out of the European single market, the world's largest borderless marketplace, which was, let's not forget, designed by the British and championed by the Conservative Prime Minister at the time, Margaret Thatcher. That is the wrong choice for Britain's interests," he will add.