The UK’s ambassador to Europe has warned that the EU will push for Britain to pay a hefty Brexit “divorce bill” after Theresa May triggers Article 50 on 29 March.

Sir Tim Barrow said EU leaders would take no notice of claims in London that Britain could quit without paying “a brass farthing”, with concern mounting that the bill could be as high as €60bn.

His warning was mirrored in comments made by EU Commission President Jean-Claude Juncker, who said the UK would have to accept the deal offered or leave with no deal, after Ms May confirmed next Wednesday as the moment Article 50 would be invoked.

Sources told The Independent that the letter Ms May will send to the EU to officially launch the Brexit process was likely to set out the broad negotiating objectives that were contained in her landmark speech at Lancaster House.

Sir Tim was giving evidence to the Commons European Scrutiny Committee when asked about a House of Lords report that concluded Britain can walk away from the EU without paying a penny. Many expect the EU’s starting point to be a call for the UK to settle a bill of up to £60bn.

Addressing the Lords report, the diplomat said: “You can imagine that counterparts have an interest in other legal opinions which have been forthcoming which offer different interpretations.”

Earlier in the day Downing Street had confirmed that the UK would trigger Article 50 on Wednesday 29 March, launching a two-year countdown to Brexit, during which a deal must be settled.

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It was Sir Tim who had the job of informing EU Council President Donald Tusk's office of the Prime Minister's plans, which allow her to meet her self-imposed deadline of the end of March to invoke the article.

Notification comes 279 days after the referendum of 23 June last year delivered a 52 per cent to 48 per cent majority in favour of withdrawal. Speaking during a visit to Swansea, Ms May said: "We are going to be out there, negotiating hard, delivering on what the British people voted for."

​Brexit Secretary David Davis said the move would initiate the Government is aiming to secure “a new, positive partnership between the UK and our friends and allies in the European Union”, but that did not stop sterling slumping against the dollar to $1.23. The pound also dived against the euro, trading 0.1 per cent down at €1.15.

At the same time in Europe, Commission President Jean-Claude Juncker warned that Britain may have to abandon its hopes of a trade deal, if it rejects the terms offered by the EU.

The UK would have “the choice to eat what's on the table or not come to the table at all”, Mr Juncker told German newspaper Bild am Sonntag.

He predicted that Britain's experience of withdrawal would bring the other 27 member states closer together, as they “see from the UK’s example that leaving the EU is a bad idea [and] fall in love with each other again and renew their vows with the European Union”.

A Government insider told The Independent that Ms May’s letter to Mr Tusk launching Brexit was likely to include the objectives for the country in leaving.

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The source said: “I suspect it will be quite a long letter setting out Britain’s position with regard to the negotiation. It’ll be a rehash of Lancaster House and the White Paper.

“There’s no mystery or magic to it. It’ll say it constitutes formal notification of our intention to withdraw from the EU, in accordance with the provisions of Article 50. Then it’ll go into a narrative outlining our position, yours sincerely Theresa May.”