Theresa May has been dealt another Brexit-related blow as the UK's ambassador to EU quit the top diplomatic post on Tuesday (3 January). Sir Ivan Rogers' decision to resign as Britain's permanent representative to the EU comes just months before the prime minister plans to start separation talks with Brussels.

The dramatic move, first reported in The Financial Times and later confirmed to IBTimes UK by a source close to the Foreign Office, also comes after Rogers' warning that it could take up to 10 years for negotiations between the UK and EU to be completed.

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The father-of-two read modern history at Balliol College, Oxford, before joining the civil service.

Rogers' career has included service as chief adviser to former Chancellor Ken Clarke, chief of staff to fellow Conservative Leon Brittan in the European Commission and principal private secretary to former Labour Prime Minister Tony Blair.

He served as European and global affairs advisor to David Cameron between 2011 and 2013 before the ex-Conservative premier promoted him to the UK's ambassador to the EU.

In the role, he was a major player in Britain's renegotiation with Brussels before the EU referendum in June, which saw the UK vote 52% to 48% to leave the bloc.

"This is a man who claimed it could take up to 10 years to agree a Brexit deal – he is far too much of a pessimist and yet another of the establishment's pro-EU Old Guard," said Arron Banks, the co-founder of the Leave EU campaign. "He has at least done the honourable thing in resigning."

Ivan Rogers
Britain's ambassador to the European Union Ivan Rogers is pictured leaving the EU Summit in Brussels on 28 June 2016 Francois Lenoir/Reuters

May has promised to invoke Article 50, the mechanism to split from the EU, by the end of March 2017. Michel Barnier, the EU Commission's chief Brexit negotiator, has said he expects talks to be completed in October 2018 and a deal ratified in March 2019.

"The resignation of somebody as experienced as Sir Ivan Rogers is a body blow to the Government's Brexit plans," said Nick Clegg, the Liberal Democrat's EU spokesman and former deputy prime minister.

"I worked for Ivan Rogers in the EU twenty years ago - then he worked for me and the rest of the Coalition Government several years later.

"Throughout all that time Ivan was always punctiliously objective and rigorous in all he did and all the advice he provided.

"If the reports are true that he has been hounded out by hostile Brexiteers in Government, it counts as a spectacular own goal.

"The government needs all the help it can get from good civil servants to deliver a workable Brexit."

Simon Tilford, deputy director of the Centre for European Reform, spoke to IBTimes UK about Rogers' resignation.

Q: How much of a blow is this to the UK government?

A: It's a blow to that bit of the government that still believes that Britain can negotiate a fairly close relationship with the EU.

I don't think it's a blow to the other wing of the government that favours – if not a clean break with the EU – but certainly a much less close relationship with it.

So it's a blow to Theresa may and Philip Hammond, I don't know if it's a blow to the government as whole because the government is so badly split on what kind of relationship Britain should be aiming for it.

I think it's bad news for Britain as a whole, it's bad news for the British economy and British interests more generally, which I think would be served by negotiating a closer arrangement as possible.

This makes this less likely unfortunately because Rogers was one of a dwindling band of officials brave enough to subject to objective scrutiny. With Rogers gone, Britain's negotiating task is that much more difficult.

We will see who they replace him with, but there are no obvious candidates and the risk is that May succumbs to pressure from some of her cabinet ministers to appoint someone who is more acceptable to the hard Brexit camp within the government.

Q: Will the EU and Michel Barnier be boosted by Rogers' departure?

A: They won't see it as a boost to them because they don't actually want a hard Brexit and very weak links between the UK and the rest of the EU.

Part of the problem with the UK is that so much of the coverage of this issue is dominated by the conjecture and prejudices of the Eurosceptic camp, who like to portray the rest of the EU, particularly France, as out to get the UK.

No one in the rest of the EU will see this is a bad news because it's going to make it even harder to come to the necessary deals and trade-offs.

Brexit European Union David Cameron