Labour is calling on the Government to set out a clear timetable for the publication of its Brexit plans, in the wake of the resignation of the UK's top civil servant in Brussels.

The party's Brexit spokesman Sir Keir Starmer demanded that Secretary of State David Davis come to the House of Commons on Monday to answer MPs' questions about the decision of Sir Ivan Rogers to quit his post just weeks before the expected start of withdrawal negotiations.

Sir Keir said the UK Permanent Representative's departure was likely to be a "significant loss" for Britain and raised "a number of serious questions" about the Government's preparations for the talks, which Prime Minister Theresa May has said she will trigger under Article 50 of the EU treaties before the end of March.

In a letter to Mr Davis, the shadow Brexit secretary said it was "frankly astonishing" that Sir Ivan had said in his resignation email that he did not yet know the Government's objectives for Brexit and "deeply concerning" that the structure and responsibilities of the negotiating team had not yet been resolved.

"Time is running out," Sir Keir warned. "It is now vital that the Government demonstrates not only that it has a plan but also that it has a clear timetable for publication... The best way to clarify these points and wider concerns many people have about this matter would be to make a statement to the House of Commons when Parliament returns on Monday."

Labour's demand came amid a war of words over Sir Ivan's explosive resignation email, in which he hit out at the "ill-founded arguments and muddled thinking" of politicians and said civil servants still did not know the Government's plans for Brexit.

Prominent Brexiteers Iain Duncan Smith and Peter Lilley accused Sir Ivan of "sour grapes", while Tory MP Dominic Raab said that the senior diplomat's "heart hasn't really been in Brexit" and his resignation would be "quietly, cautiously and respectfully welcomed at the top of Government".

Ex-cabinet minister Mr Duncan Smith suggested that Sir Ivan had lost ministers' confidence because it appeared he had a hand in the leaking of an earlier warning that a post-Brexit trade deal could take a decade to finalise.

"The truth is, I think there's a little bit of sour grapes going on here because he's not really included much in the discussion about how they are going to go about this negotiation, partly because ... I think ministers don't fully trust him," the former Conservative leader told Sky News.

But the Foreign Office's former top civil servant Lord Ricketts attacked the "denigration" of the long-serving mandarin and dismissed suggestions that he was responsible for leaks as "a smear".

"I don't think it's sour grapes, I think it's a sense that there is a huge task out here. I am really concerned about this undertone of denigration of Ivan as a person, and this feeling that it has got to be 'one of us' next time. That's a complete misunderstanding of what civil servants are for," Lord Ricketts told BBC Radio 4's World at One.

And the head of the senior civil servants' union warned Mrs May not to choose a "yes man" to head the UK Representation to the EU (UKREP).

FDA union general secretary David Penman said: "It doesn't surprise me that some politicians are calling for pro-Brexit civil servants to be appointed. What surprises me is the deafening silence from ministers who should be taking to the airwaves to defend the integrity and capability of the impartial civil service.

"If the civil service is to deliver a successful Brexit negotiation, the recipe for that success is unlikely to be to starve it of resources, lack clarity of objective and be surrounded with yes men and women who will not speak truth unto power."

Former Foreign Office minister Alistair Burt - who campaigned for Remain in the referendum - backed calls for a Commons statement, telling the ConservativeHome website: "A very senior UK patriot has chosen to leave his post, rather than continue down a path of which he fears for our country. This requires a Government statement and explanation next week - and should induce further urgency into our preparations, and the base for our negotiations."

Following a Commons vote last month, Mrs May has promised to publish details of her Brexit plans before invoking Article 50, but Mr Davis has indicated this will not come before February at the earliest. Labour insists the plans must be published in time for proper scrutiny by the House of Commons, devolved administrations and relevant Select Committees.

Brussels officials said Sir Ivan's resignation meant the UK had lost a "professional" diplomat who had always "loyally defended" his Government.

The European Commission said it regretted the loss of a "very knowledgeable" envoy and indicated that Sir Ivan had been a tough negotiator in wrangles with Brussels.

And the European Parliament's chief Brexit negotiator, Guy Verhofstadt, described him as "a much-respected UK civil servant in Brussels who knew what he was talking about".

Jonathan Powell, Tony Blair's former chief of staff and an ex-diplomat, warned the Prime Minister against hiring a pro-Brexit successor to Sir Ivan.

Appointing a "patsy" who does not explain plainly what the other side is thinking will doom the Brexit negotiations to failure as ministers will be operating in a "fantasy land" about what is achievable, he told BBC Radio 4's Today.

In his resignation letter, Sir Ivan criticised politicians and urged his civil servants to continue to challenge ministers and "speak the truth to those in power".

"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," he wrote.

Sir Ivan could still take part in a meeting on January 10 of the Coreper II group - made up of the permanent representatives from each member state. Officials at the UK mission in Brussels said no formal date had yet been fixed for his departure.