LONDON — The United Kingdom filed for divorce from the European Union today. Britain’s top envoy to the EU, Tim Barrow, hand-delivered a letter to European Council President Donald Tusk formally triggering a two-year countdown to the final split.

“Today the government acts on the democratic will of the British people.” Prime Minister Theresa May told lawmakers in the House of Commons, adding, “This is an historic moment from which there can be no turning back.”

Tusk tweeted that “after nine months the UK has delivered,” followed by a photo of Barrow handing him the letter in Brussels.

There is “no reason to pretend this is a happy day,” Tusk told reporters later, emphasizing that the priority now is to minimize costs for EU citizens and member states.

For Britons who voted 52 to 48 percent to leave the bloc nine months ago, it was a time for celebration.

Former U.K. Independence Party leader Nigel Farage, who campaigned for years to take Brexit from fringe cause to reality, said Britain had passed “the point of no return.”

For “remain” campaigners, it was time to fight for a divorce settlement that preserves what they see as key benefits of EU membership, including free trade in goods and services and the right to live and work anywhere in the bloc.

May’s letter to Tusk was polite and conciliatory, saying that Britons want to remain “committed partners and allies to our friends across the continent.”

Germany’s Foreign Ministry said Britain would remain a “close partner and friend” of the EU, but that “being a close friend is not the same as being part of the family.”

It’s not even certain that the United Kingdom will survive intact. Scotland’s parliament voted Tuesday to back a referendum on independence within two years.