BIRMINGHAM, England — Britain’s formal talks on quitting the European Union will begin by the end of March, Prime Minister Theresa May said on Sunday, in an announcement that could mean a British departure from the 28-nation bloc by the spring of 2019.
Speaking ahead of her party’s annual convention, Mrs. May set out a more detailed timeline for initiating exit negotiations that are governed by a two-year deadline unless all members of the bloc agree to prolong them.
Previously, Mrs. May had said only that the talks, under Article 50 of the European Union’s treaty, would not begin before the end of this year. The delay is designed to give the government time to work out its negotiating position.
But speaking to the BBC on Sunday, Mrs. May said that Article 50 would be set into motion “before the end of March,” while giving little more detail about the type of ties she wants with other European nations after a British withdrawal, known as Brexit.
Following the vote in a British referendum in June to leave the European Union, the government still lacks a clear strategy for Brexit, which is likely to precipitate the biggest change in the country’s relationship with the rest of the world since World War II.
On Sunday, Mrs. May also announced plans to start the domestic legislative process for Brexit next year by repealing an act of Parliament, the 1972 European Communities Act, that allowed Britain to join the European Union’s predecessor.
Although this new legal step would not come into effect until Britain actually left the bloc, it would transfer European legislation — including laws to protect labor rights — into British law. Parliament would then be able to decide at a later point which laws to keep.
Despite Mrs. May’s latest comments, the shape of Britain’s desired new relationship with the European Union remains unclear, amid signs of deep divisions within her cabinet over whether to try to keep close economic ties or to go for a more fundamental break, particularly in order to curb migration from the Continent.
Britain has so far not even said it wants to quit Europe’s Customs Union, which lays down tariff rules but which prevents a country from striking unilateral free trade deals with non-European nations.
Nevertheless, the stress Mrs. May has given to controlling migration, which proved a significant issue in the June referendum, suggests that the country could be headed into a “hard Brexit” — one that would allow it to curb immigration even if that meant less favorable access to a European single market that currently numbers around 500 million consumers.
Such a prospect has prompted warnings from manufacturers, including carmakers that fear they may face tariffs, and from financial services companies that worry about their ability to do business across Europe from London.
Last week, Carlos Ghosn, the chief executive of Nissan, said he would be unable to make investment decisions in Britain unless the government guaranteed compensation for any tariffs that might be imposed after Brexit.
Still, the outcome of June’s referendum was interpreted by many politicians, including Mrs. May, as a rejection of the European Union’s policy in support of the free movement of people, which has allowed hundreds of thousands of people from Southern and Eastern Europe to settle in Britain.
Mrs. May served as home secretary for six years and devoted much of that time to an ultimately ineffective attempt to cut immigration.
Ideally, Britain would like to regain control of the ability to curb migration from Continental Europe while also keeping full access to the European Union’s single market.
In an interview in The Sun published on Saturday, Boris Johnson, the foreign secretary, argued that Britain’s policy was “having our cake and eating it.”
But a succession of European politicians have made it clear that a trade-off is required from Britain. The European Union aims to guarantee the free movement of goods, capital, services and people across its frontiers, and for many of Europe’s policy makers it would be a betrayal to allow Britain to enjoy the economic benefits while rejecting the free movement of people.
In a recent interview with the BBC, the Italian prime minister, Matteo Renzi, said it would be “impossible” to give British people more rights than others outside the European Union.
The president of the European Central Bank, Mario Draghi, has said that Britain should not be granted any special favors on single-market access and that “any outcome should ensure that all participants are subject to the same rules.” That message has also been echoed by the French and German finance ministers, Michel Sapin and Wolfgang Schäuble.
In Britain, leading supporters of Brexit, including Mr. Johnson and the secretary of state for international trade, Liam Fox, are believed to be pressing for a hard Brexit that would take Britain out of the European single market and Europe’s customs union but give it the power to negotiate its own trade deals.
However, the chancellor of the Exchequer, Philip Hammond, appears to be pressing for the best possible access to the single market, reflecting the views of a number of critical sectors of the economy.