The UK's ambassador to the EU, Sir Ivan Rogers, resigned just three months before the UK intends to start formal talks to leave the bloc, the British government said Tuesday.

In his resignation email to the staff at UKRep, the organization tasked with representing the UK in negotiations with the EU, Rogers urged his colleagues to continue to speak up even when their views were not welcome.

"I hope you will continue to challenge ill-founded arguments and muddled thinking and that you will never be afraid to speak the truth to those in power," wrote Rogers in the email.

Rogers continued by criticizing the UK's lack of preparation for the proceedings.

"Serious multilateral negotiating experience is in short supply in Whitehall, and that is not the case in the Commission or in the Council," wrote Rogers.

Not a surprise

The "Financial Times" had earlier reported that Rogers told staff he would be resigning, but did not give a reason for his resignation in a letter to his staff.

"His resignation is not a surprise for those who work with him," a European diplomat told news agency Agence France-Presse.

"He was very competent, but not convinced by the Brexit decision and the British government line, leading the UK into an area of dangerous uncertainty," the source added.

The chairman of parliament's Brexit committee, Hilary Benn, said news of Rogers' departure is "not a good thing."

"This is a time for continuity and experience because this going to be a very complex, a very challenging, a very difficult negotiation," Benn told BBC radio.

Last month, the BBC reported that Rogers told UK ministers that EU countries believe it would take 10 years before they could form a new trade deal with Britain.

British Prime Minister Theresa May's spokesman rejected the report at the time, saying the deal could be done within the two-year divorce negotiation time window.

Britain's Foreign Office and Downing Street did not immediately comment on the reports.

Appointed by former Prime Minister David Cameron as the UK's envoy to Brussels in November 2013, Rogers is one of Britain's most experienced diplomats on EU affairs. He was awarded a knighthood in 2016 for services relating to European policy.

Brexit uncertainty

The UK's vote to leave the EU has opened a large number of questions including whether the UK will still have access to the single European market or what will happen with immigration and the future rights of EU citizens already living in Great Britain.

Preparations for the UK's divorce from the EU after the country's referendum in June have been reportedly rocky and Rogers' departure is likely to add to tensions.

In the June referendum, 52 percent voted for Britain to leave the EU. May has said she will trigger Article 50 of the EU's Lisbon Treaty - which gives formal notification of Britain's intention to leave the bloc - by the end of March.

In early January, British Supreme Court justices are due to rule on who can rightfully trigger Article 50 - the government or parliament.

rs/rc (AFP, Reuters)