Foreign Secretary Boris Johnson has warned that Brexit negotiations will be tough, saying that some plaster “may fall off the ceiling”.

But the arch-Brexiteer predicted that Theresa May will pull off a successful outcome and “usher in a new era of free trade deals”, in a speech in London.

His comments came as Mrs May held a working dinner with European Commission president Jean-Claude Juncker and the bloc's chief negotiator Michel Barnier in Downing Street.

On Saturday the leaders of the other 27 EU countries will discuss their draft guidelines for negotiations, which reject the UK's pleas for parallel trade and divorce talks.

Amid growing concerns about the negotiations, Brexit Secretary David Davis tried to reassure business that the UK would secure a speedy deal to to protect the rights of EU citizens living in UK.

But Mrs May also came under pressure from former Prime Minister David Cameron who urged the UK to agree a "divorce bill" with the EU before trade talks can start.

Experts predict the UK's 'divorce bill' could top £50 billion.

Mr Barnier has also insisted that the UK "settle the accounts" before beginning talks on a future UK-EU trading relationship.

Mr Cameron also raised eyebrows by claiming that the EU referendum had brought to an end a "poisoning" of UK politics.

No 10 said that the Prime Minister wanted to build a "real and special relationship" with the EU post-Brexit.

She is also expected to reiterate her wish for an early deal on the rights of EU citizens living in the UK and British ex-pats in EU countries.

Meanwhile, one of Deutsche Bank's top executives has said that nearly half of its UK-based jobs are at risk of being shifted out of the country as a result of Brexit

Chief regulatory officer Sylvie Matherat suggested that 4,000 back and front office positions could be forced to relocate in order to serve EU clients if passporting rights - which give banks access to the EU's single market for financial services - are lost.