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Theresa May has met the EU's chief Brexit negotiator for talks in Downing Street in the run-up to a crucial summit of the remaining 27 EU members.

She had a working dinner with Michel Barnier and European Commission President Jean-Claude Juncker in No 10.

Downing Street said Mrs May reiterated the UK's aim of building a "deep and special partnership" after Brexit.

Reuters quoted a Commission spokeswoman saying they discussed the process of the UK's withdrawal from the EU.

On Saturday, EU leaders meet to agree their key negotiating principles based on draft guidelines issued last month. Official talks will not begin until after the general election on 8 June.

The UK is on course to leave the EU in March 2019, after Mrs May triggered Article 50 last month.

Mr Barnier, a former EU Commissioner, has said Brexit negotiations must be concluded within 18 months to allow for any settlement to be approved by the UK, other EU members and the European Parliament.

The EU wants the terms of the UK's exit to be decided before any discussion of a future trade relationship while Mrs May wants to the two issues to be dealt with simultaneously.

Addressing foreign diplomats in central London on Wednesday, Foreign Secretary Boris Johnson said the government had a "clear plan" for Brexit.

"Though I have no doubt that the negotiations will be tough and some plaster may fall off the ceiling, I am also sure that Theresa May can pull it off, and usher in a new era of free trade deals," he said.

Amid continued speculation about the size of the so-called "divorce bill" the EU is seeking, former PM David Cameron said he hoped that the two sides would be able to agree a figure early on in the negotiations.

Speaking at a conference in Thailand, he said "of course we accept some liabilities for this membership we've had for 40 years, just as we have a claim on some of the assets that we've paid into".

"And I think we can settle the principles of that and then get on with the nature of the relationship."