The European Union's chief negotiator has said "I can't negotiate with myself", as he warned Britain may be running out of time to reach a Brexit deal.

Michel Barnier said Theresa May's government must begin talks "very quickly" as he noted that in three months since Article 50 was triggered "we haven't progressed" toward reaching a deal before the looming March 2019 deadline.

The Prime Minister has talked up her plans to get on with negotiations, due to begin within days.

She "has directed that the procedures for preparing the negotiations for the formal withdrawal from the European Union should start as soon as possible," the Government told the European Commission on Friday.

Mr Barnier told the Financial Times: "My preoccupation is that time is passing, it is passing quicker than anyone believes because the subjects we have to deal with are extraordinarily complex.

"It will take us several months to draw out the conditions of an orderly withdrawal. Let’s not waste time.

"I’ll say it clearly: there’s no spirit of revenge, no punishment, no naivety either. And there is truth. Truth on what Brexit means, what leaving the EU signifies by its consequences. The citizens have the right to know."

"Lots" of Britons underestimated what those consequences would be, he added.

In pictures: European parliament Brexit discussions Show all 12 1 /12 In pictures: European parliament Brexit discussions In pictures: European parliament Brexit discussions European commission member in charge of Brexit negotiations with Britain, French Michel Barnier listens at the President of the European Commission Jean-Claude Juncker speaking at the European Parliament in Strasbourg Getty Images In pictures: European parliament Brexit discussions Frank-Walter Steinmeier, President of the Federal Republic of Germany, delivers his speech at the European Parliament in Strasbourg EPA In pictures: European parliament Brexit discussions European Union's chief Brexit negotiator Guy Verhofstadt, President of the Group of the Alliance of Liberals and Democrats for Europe (ALDE), addresses the European Parliament during a debate on Brexit priorities and the upcomming talks on the UK's withdrawal from the EU Reuters In pictures: European parliament Brexit discussions Michel Barnier, European Chief Negotiator for Brexit reacts during a meeting at the European Parliament in Strasbourg EPA In pictures: European parliament Brexit discussions Member of the European Parliament and former leader of the anti-EU UK Independence Party (UKIP) Nigel Farage wears socks with Union Jack flag at the European Parliament in Strasbourg Getty Images In pictures: European parliament Brexit discussions Nigel Farage, United Kingdom Independence Party (UKIP) member and MEP, addresses the European Parliament during a debate on Brexit priorities and the upcoming talks on the UK's withdrawal from the EU Reuters In pictures: European parliament Brexit discussions European commission member in charge of Brexit negotiations with Britain, French Michel Barnier gestures during speeches at the European Parliament in Strasbourg Getty In pictures: European parliament Brexit discussions The President of the European Commission Jean-Claude Juncker (L) speaks with European commission member in charge of Brexit negotiations with Britain, French Michel Barnier at the European Parliament in Strasbourg Getty In pictures: European parliament Brexit discussions European Union's chief Brexit negotiator Guy Verhofstadt, President of the Group of the Alliance of Liberals and Democrats for Europe (ALDE), addresses the European Parliament during a debate on Brexit priorities and the upcomming talks on the UK's withdrawal from the EU Reuters In pictures: European parliament Brexit discussions Member of the European Parliament and former leader of the anti-EU UK Independence Party (UKIP) Nigel Farage gestures during speeches at the European Parliament in Strasbourg, eastern France, on April 5, 2017. The European Parliament will on April 5 lay down its "red lines" for negotiations over a Brexit deal, on which the assembly will have the final say in two years' time. / AFP PHOTO / Sebastien BozonSEBASTIEN BOZON/AFP/Getty Images Getty In pictures: European parliament Brexit discussions German president Frank-Walter Steinmeier delivers a speech during a plenary session at the European Parliament in Strasbourg Getty In pictures: European parliament Brexit discussions The European Parliament in Strasbourg, eastern France Getty Images

It comes as a report claimed Labour and Conservative MPs had met for secret talks aimed at urging Ms May to take a cross-party approach to Brexit.

The Scottish Conservatives' leader Ruth Davidson, whose influence has increased dramatically with the election of 13 Tories north of the border, has broken ranks to say: "This isn't just going to be a Tory Brexit."

Ms May's position in the Commons was weakened as a result of losing her majority in the general election, fuelling speculation she will be forced to alter her approach to the Brexit negotiations.