Ivan Rogers told staff on Tuesday afternoon that he would be step down from his post early, the FT said. He did not explain the reasons for the move, according to people who have seen the his note to diplomatic staff, the FT said.
Britain 'will allow EU citizens to stay' after Brexit
May has said she will trigger formal Brexit talks with the rest of the EU by the end of March.
Rogers, 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.
Downing Street and Britain's Foreign Office did not immediately comment on the FT report.
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