A LEAKED email from the UK ambassador to the European Union outlining the reasons for his resignation has lifted a lid on the chaotic dealings behind the scenes in government less than three months before negotiations are due to begin.

The UK’s top diplomat in Brussels Sir Ivan Rogers resigned on Tuesday in a shock move that caught the government off guard and disappointed many who knew of his decades of experience.

His 1400-word email to staff outlining the reasons for quitting says the government does not yet know what it’s negotiating for and urges them to challenge “muddled” thinking at the highest levels.

“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,” he wrote in the email published in full by the BBC.

“I hope that you will support each other in those difficult moments where you have to deliver messages that are disagreeable to those who need to hear them.”

Sir Ivan is widely seen as one of the UK’s most experienced diplomats in Europe and had previously warned the process could take a decade of negotiations. He has criticised the “control freak” Home Office for their attitude to the negotiations, The Times reports.

His resignation email also reveals what many outside government had feared in terms of priorities — that there are none.

“We do not yet know what the government will set as negotiating objectives for the UK’s relationship with the EU after exit.”

He added that the swath of elections in the Netherlands, France, Germany and Italy also mean the UK does not know who it will be negotiating with.

“There is much we will not know until later this year about the political shape of the EU itself, and who the political protagonists in any negotiation with the UK will be,” he wrote.

UK Prime Minister Theresa May said the government will trigger Article 50 which begins the two-year Brexit negotiations by the end of March 2017, meaning the UK will leave the EU by March 2019 which is ahead of the next general election.

However she has refused to lay out any details of the plan, only saying that she will work towards a “red white and blue Brexit” for the UK. Major questions around whether the UK will remain part of the single market remain unanswered.

Critics of Sir Ivan say his “pessimistic” attitude will provide a chance for the Prime Minister to appoint someone who “believes in Brexit”.

The email also issued a final rallying call to staff saying their expertise will be needed to forge new deals that continue to provide great opportunity if done correctly.

“Serious multilateral negotiating experience is in short supply in Whitehall, and that is not the case in the Commission or in the Council.”

“Contrary to the beliefs of some, free trade does not just happen when it is not thwarted by authorities: increasing market access to other markets and consumer choice in our own, depends on the deals, multilateral, plurilateral and bilateral that we strike, and the terms that we agree,” he said.

He urged them to “stick with it” and said the “combination of immense creativity with realism ground in negotiating experience is needed more than ever right now.”