Former deputy prime minister Nick Clegg is concerned about EU's future
Speaking ahead of the Prime Minister's talks with Donald Trump in Washington on Friday, Mr Clegg will name the new US president 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.
At a conference in Brussels on Tuesday, the former Liberal Democrat leader will warn Mrs May to put Britain's interests first at the White House on Friday, and not to be drawn into the president's "nationalist tactics to undermine the EU".
He will accuse Mr Trump of "effectively colluding" with Russian leader Vladimir Putin to undermine the security and prosperity of Europe, said party aides.
Mr Clegg is expected to tell the E!Sharp conference: "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.
Mr Clegg will name Donald Trump as part of an "axis of aggressive nationalism"
May's Brexit speech: Europe reacts
Tue, January 17, 2017
Politicians and celebrities tweet their reaction as Theresa May unveils her 12 point plan for Britain leaving the EU.
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The British Prime Minister Delivers Her Brexit Speech
"This has long been the stated ambition of the most hardline Brexiteers, and was repeated at the meeting of populist parties held in (German city) Koblenz this weekend.
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"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.
Clegg will warn Mrs May to put Britain's interests first at the White House on Friday
"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."