Sir Ivan Rogers has resigned from the civil service entirely, just days after announcing he would be quitting his post as UK ambassador to the European Union.
The Foreign Office (FCO) confirmed that he was not seeking any further civil service job.
An FCO spokeswoman said: “Sir Ivan Rogers resigned as UK Permanent Representative to Brussels on 3 January.
“He did not seek any further civil service appointment and has therefore resigned from the civil service with immediate effect.
”We are grateful for Sir Ivan’s work in Brussels and across a number of other senior positions in the civil service.”
He unexpectedly quit his ambassador role on Tuesday just months after he sparked controversy by warning the government that a post-Brexit trade deal could take a decade to finalise, and even then may fail to get ratified by member states.
In a lengthy farewell email to his staff, obtained by The Times, Sir Ivan revealed that civil servants still do not know the Government’s Brexit priorities and that “serious multilateral negotiating experience is in short supply in Whitehall” - unlike in Brussels.
He criticised “ill-founded arguments and muddled thinking” over Brexit policy.
He stressed the need for expert civil servants to play a central role in the negotiations and urged his staff to tell ministers the true opinions of the other 27 member states “even where this is uncomfortable”.
He is to be replaced by Sir Tim Barrow.
Rogers’ actions come just months before Brexit negotiations are due to take place.
Theresa May has said she intends to trigger Article 50, the formal process of leaving the EU and beginning negotiations with Brussels, by the end of March.