Though the European Union is not keen to see the United Kingdom leave, it said it is ready to move forward. She added that British Prime Minister Theresa May had assured her it would in a phone conversation on Tuesday.
But he said the invoking of Article 50 was not "a happy day" for him, for the European Union or for Britain, adding: "There is nothing to win in this process - and I am talking about both sides". The two sides now have until March 2019 to agree on a divorce settlement and - if possible - establish a new relationship between Britain, the world's fifth-largest economy, and the European Union, a vast single market stretching over 27 countries and half a billion people.
The EU says Britain can't leave without settling its bill, paying up for the U.K.'s share of staff pensions and projects it has already agreed to fund.
"I can still, to be honest with you, scarcely believe today has come", he said.
The divorce proceedings are supposed to be completed within two years, but Britain wants to have a parallel process during which the future trading relationship with the European Union, and by extension, Ireland, is opened up. Unless both parties agree to prolong the deadline for talks, the United Kingdom will leave on 29 March 2019.
This is published unedited from the IANS feed.
In the coming days the EU's negotiating guidelines will be given to Taoiseach Enda Kenny and the other leaders of the remaining member states, laying the ground rules for the talks to come.
"In my opinion, this is the greatest moment in modern British history", said Brendan Chilton, general secretary of the pro-Brexit group Labour Leave. "It would help both sides to minimise unnecessary disruption if we agree this principle early in the process".
Going forward, May said, the British government will seek to control immigration but maintain trade ties, in line with the wishes of British voters.
The U.K.'s borders with the European Union, particularly the only land frontier between Northern Ireland and the Republic of Ireland, will need to be urgently addressed.
"Britain is going to change as a result of leaving the EU. We also have an important responsibility to make sure that nothing is done to jeopardise the peace process in Northern Ireland, and to continue to uphold the Belfast Agreement".
Today Mr Tusk promised to begin arrangements for an "orderly withdrawal" for the United Kingdom, but said there was nothing for either side to gain from the two years of negotiations to come, which would be no more than an effort at "damage control".