LONDON (AP) — Britain's outgoing ambassador to the European Union has strongly criticized the government's approach to Brexit negotiations in a farewell email to his staff.

Ivan Rogers said the British approach to the upcoming Brexit talks has been hindered by "ill-founded arguments" and "muddled thinking."

His harsh critiques were made public when the email was published by British media Wednesday. He had resigned the day before, months earlier than expected.

In the blunt email, Rogers says top civil servants preparing for talks with EU negotiators still don't know the British government's priorities.

Prime Minister Theresa May has said Britain will formally trigger exit talks by the end of March.

Rogers had earlier said it would take longer than expected to reach new trade deals and that the process might fail.