THERESA May has made history with the stroke of a pen as she formally starts the process of Britain's withdrawal from the EU, telling the country it is now the time to unite.

The two years of talks with Brussels are set to be the most complicated negotiations the UK Government has engaged in since World War Two.

Ahead of a Commons statement setting out her aims and priorities for the forthcoming process, the Prime Minister urged Britain to come together as it faced its “momentous journey” after a 44-yearlong relationship with the EU.

“When I sit around the negotiating table in the months ahead, I will represent every person in the whole United Kingdom: young and old; rich and poor; city; town; country and all the villages and hamlets in between. And yes, those EU nationals who have made this country their home.

“It is my fierce determination to get the right deal for every single person in this country. For, as we face the opportunities ahead of us on this momentous journey, our shared values, interests and ambitions can - and must - bring us together.”

Mrs May said that everyone in Britain wanted to see a country that was stronger, fairer and more secure; a truly Global Britain that built relationships with old friends and new allies around the world.

“These are the ambitions of this Government’s Plan for Britain; ambitions that unite us, so that we are no longer defined by the vote we cast, but by our determination to make a success of the result.”

She added: “We are one great Union of people and nations with a proud history and a bright future. And, now that the decision has been made to leave the EU, it is time to come together.”

Signed personally by Mrs May, a so-called "wet signature" in Civil Service jargon, the exit letter will be delivered to Donald Tusk, the European Council President, by Sir Tim Barrow, the British ambassador to the EU, at around 12.30pm UK time as the PM stands up to deliver her statement to MPs.

Within the following 48 hours, the European Commission is expected to issue "draft negotiation guidelines," which will be sent to the 27 remaining states for consultation.

The EU27 leaders will meet on April 29 at an extraordinary European Council summit to agree a mandate for chief negotiator Michel Barnier and clear the way for talks to begin in earnest in May, following the French elections.

On Tuesday night ahead of the letter being delivered, the PM called not only Mr Tusk but also Jean-Claude Juncker, President of the Commission, and Angela Merkel, the German Chancellor, to update them ahead of the formal notification of withdrawal.

"In separate calls, they agreed that a strong EU was in everyone’s interests and that the UK would remain a close and committed ally,” explained a No 10 spokesman.

“They also agreed on the importance of entering into negotiations in a constructive and positive spirit and of ensuring a smooth and orderly exit process,” he added.

Mr Juncker said his conversation had been "good and constructive". Earlier, the Commission President made clear to Sadiq Khan, the London Mayor, making an official visit to Brussels, that the EU wanted to negotiate with the UK in a "fair and friendly" way.

The talks ahead will have two core issues to resolve: the terms of Britain's withdrawal from the EU and the arrangements for a future trade deal.

In addition, there might have to be a third strand of talks, involving a "transitional arrangement," covering the period between the moment of departure and new trade rules taking effect.

On Thursday, a White Paper will be produced on the Great Repeal Bill, the legislation that will turn more than 40 years of EU regulations into domestic law.

At Westminster, Jeremy Corbyn said Britain was now embarked on change but stressed how Labour was determined to ensure that no one and no community would be left behind.

"It will be a national failure of historic proportions if the Prime Minister comes back from Brussels without having secured protection for jobs and living standards. That's why Labour has set the clear priorities of full access to the European market, rights at work and environmental protection.

"And we will hold the Government to account every step of the way," he added.