"This is an historic moment from which there can be no turning back," says Theresa May

Britain has triggered its departure from the E.U., commencing two years of negotiations with its European partners.

The letter, signed by Prime Minister Theresa May late on Tuesday, was handed over by Sir Tim Barrow, the U.K.’s permanent representative to the E.U., to European Council president Donald Tusk in Brussels.

The handover will propel both Britain and the E.U. into a new territory, as the country becomes the first nation in history to trigger Article 50, the six-paragraph-long section of the Lisbon Treaty, briefly outlining the process for exiting the union.

Also Read The referendum: Brexit and after

Spotlight now on U.K.-E.U. talks

With events now set in motion to take Britain out of the E.U., the spotlight will fall on the negotiating process, the terms agreed, and the ways in which the country will build its post-EU future.

While Ms. May has insisted that the government aims to deliver a “smooth and orderly Brexit” and reach an agreement within two years, many remain sceptical. They point to the seven years the EU and Canada took to reach a free trade deal. The EU has indicated in the past that a deal would have to be agreed within 18 months to give enough time for all the relevant bodies and national Parliaments to get on board.

In the past, Ms. May had indicated that Britain would prefer to leave the EU with no deal rather than a bad deal, though critics have pointed to a past analysis by the Treasury department that leaving the union on World Trade Organization’s terms (in the absence of a deal within the two-year timetable) could knock as much as 7.5% off GDP.

In her letter to Mr. Tusk, Ms. May emphasised her eagerness to get the deal. “We must therefore work hard to avoid this outcome,” she wrote.

“The Commission’s approach will be detailed, painstaking and business-like… Britain’s priority should not be the divorce bill but the future trade deal,” said Lord Peter Mandelson, a former EU trade commissioner and chair at Global Counsel.

“The government should seek to secure a trade deal with the EU that ensures reciprocal market access and is as close as possible to our existing arrangements,” said Mark Boleat, the policy chairman of the City of London Corporation, adding that a transitional deal was needed early in the negotiations to provide businesses with clarity and reassurance.

Right to remain

The government will also face a battle going forward over issues such as the right to remain of EU citizens already in the U.K. In her letter to Mr. Tusk, Ms. May called for Britain and Europe to strike an “early agreement” on the rights of EU citizens in Britain, and U.K. citizens across Europe.

There will also be a domestic battle over what EU laws Britain chooses to apply to itself once it leaves the union, as well as other policy changes it will bring in to further the trade deals it hopes to make outside the EU.

On Wednesday, Jeremy Corbyn, leader of the Labour Party, called on the Prime Minister to “listen, consult and represent” the whole country, accusing the government of wanting to change it to a “tax dodgers’ paradise”. “Labour will not give this government a freehand,” he said. Ms. May said she would “represent every person in the whole United Kingdom” to create a “fairer… truly Global Britain that gets out and builds relationships with old friends and new allies around the world.”

The triggering of Brexit has also brought to the fore questions about the future of the countries that make up the U.K. In a heated ‘Prime Minister’s Questions’ just before Ms. May’s historic announcement, she battled questions on pledges made earlier to consult with members of the devolved governments on the terms of Brexit talks. Ms. May shot back, telling that she had always been clear that the negotiations would be conducted on behalf of a united nation, and that now was not the time for questioning the nation’s unity.

However, the issue is unlikely to go away following Tuesday’s vote by the Scottish Parliament to back calls for a second referendum on independence. In her letter to Mr. Tusk, Ms. May said the government expected that the Brexit process would result in “a significant increase in the decision-making power of each devolved administration”. She added that the government would be looking to avoid a hard border between the Republic of Ireland (an EU member state) and Northern Ireland (part of the U.K.).

“We can choose to say the task ahead is too great. We can choose to turn our face to the past and believe it can’t be done. Or we can look forward with optimism and hope — and to believe in the enduring power of the British spirit,” said Mrs May.

The biggest challenge may now prove to be uniting the country, with many in the Remain and Leave camps entrenched in their views about the future and each other. However, according to recent polling by YouGov, only 21% of people want to see the result of the referendum overturned or ignored.