LONDON • Britain's ambassador to the European Union (EU) has resigned just three months before Prime Minister Theresa May starts formal Brexit negotiations.

Sir Ivan Rogers, Britain's permanent representative to the EU, told staff yesterday he would step down from his post early, said the Financial Times (FT), which was the first to report the resignation.

He did not explain why he was resigning, according to people who have seen his note to diplomatic staff, the FT said. Two sources who asked for anonymity confirmed the report that he had resigned.

"This weakens May's ability to get a good EU deal," said Mr Charles Grant, director of the Centre for European Reform think-tank. "Ivan Rogers was one of the very few people at the top of the British government who understand the EU."

The resignation is the second by a senior British EU official in the wake of the referendum. Lord Jonathan Hill quit as Britain's European commissioner in June.

Mrs May has said she will trigger formal Brexit talks - likely to be among the most complicated negotiations in post-World War II European history - by the end of March.

Britons' vote to leave the bloc has opened a huge number of questions, including whether exporters will keep tariff-free access to the single European market and whether British-based banks will still be able to serve continental clients, not to mention immigration and the future rights of the many EU citizens already living in Britain.

Sir Ivan, appointed by former prime minister David Cameron as Britain's envoy to Brussels in November 2013, is one of Britain's most experienced diplomats on EU affairs. He had worked in Downing Street, the British Treasury and the European Commission and at Citigroup and Barclays Capital.

But after Mr Cameron lost the June 23 Brexit vote, Sir Ivan drew criticism for lacking ambition in Mr Cameron's 2015 attempt to redefine Britain's relationship with the bloc.

He warned Mrs May's ministers that the European consensus was that a trade deal with the EU might not be done until the early to mid-2020s and that national parliaments could ultimately reject it, the BBC reported last month.

REUTERS