The most likely location for the talks involving teams led by Michel Barnier for the EU and a yet-to-be-identified minister for the British government is the Cabinet Office in Whitehall.

Brussels took centre stage over the past three years as the UK remained an EU member state.

The EU’s control over press conferences at the European commission’s Berlaymont headquarters irritated the former Brexit secretary David Davis, who avoided visiting due to Barnier’s tendency to monopolise media coverage.

With the UK negotiating as a “third country”, the rules are due to change. For 11 months after withdrawal on 31 January, the UK will stay in the EU’s single market and customs union. But it will no longer be a member state and officials in Brussels expect the location of the talks to be split.

The shift is expected to be confirmed in “talks about talks” due between the UK and EU negotiators in February, sources said.

A government spokesman said: “The political declaration makes clear that the UK and EU have to jointly agree the scheduling of talks. More details will be set out in due course.”

Negotiations on the future relationship are expected to start in earnest in early March. EU member states are due to adopt their negotiating position on issues such as trade in goods, fisheries, security and level playing field demands on 25 February after the publication of a draft paper in the first week of the month.

A leaked diplomatic note seen by the Guardian said: “The mandate will contain no surprises and will be based on the political declaration.

“Topics such as fisheries or a level playing field will be discussed [internally] in January. These discussions will be based on slide presentations from the European commission instead of official drafts. That should give a sense of the sensitivities of member countries and make progress easier.”

There is no expectation that the 11-month transition period will be extended beyond the end of 2020. An EU official said: “The member states have been told it is not happening.”

But the June summit of EU leaders – without UK involvement – is expected to be a pivotal point in the negotiations and will signal whether hope remains of securing at least a “bare bones” deal on trade, fishing rights and security by the end of the year.

On trade in goods, the EU’s negotiating position is yet to be finalised, with seminars for diplomats organised from 8 January up to the end of the month.

But the level playing field demands in the 2018 Irish protocol, which would have tied the UK to the EU’s customs union, are seen as a baseline below which Brussels will not go.

Theresa May had committed the UK to dynamically aligning with future EU changes to competition and state aid rules in the “Irish backstop”.

The commitment on environmental protections and social and labour standards was to not lower them.

Sources suggested the French government might seek to toughen the demands further during internal EU discussions in February.

“The French said at the time that they negotiated the Irish backstop and its provisions in the name of peace, and that this would be different,” said one EU source. “The aim in February will be to have everyone owning the strategy.”

An EU source said: “The issue is not whether the UK will seek to undercut the EU but whether they could, and therefore it holds us back in our own policymaking. That’s the problem.”

Suggestions from Whitehall that the UK would accept tariffs on some goods as the price for diverging from EU standards have concerned officials in Brussels. “If we start talking about tariffs, there is no chance of a trade deal by the end of the year, as it becomes a very complicated discussion among the member states,” one source said.

A major strand of the talks is expected to be related to security issues. “How do we extradite someone, for example?” asked one EU source. “It won’t be the European arrest warrant, but we need something between that and nothing. It has to be there – it would be unforgivable if it was not.

“There also needs to be agreement on sanctions. You can just coordinate, with the UK tagging on to EU decisions, but that makes sanctions less likely to be supported in the courts. You need a formal agreement.”

On fisheries, the political declaration obliges the EU and the UK to make “best endeavours” to agree on future access to British waters by 1 July, but Brussels sources are sceptical as to whether such a deal can be struck in that time.

“Without an agreement on fish, there will not be a deal – the price for a trade deal is the level playing field demands and fishing rights,” said an EU source. “But in reality, we don’t have to agree it by the summer, just the end of the year.”

Gerard van Balsfoort, the chair of the European Fisheries Alliance, a lobby group representing the fishing fleets of the member states most affected by Brexit, said there needed to be certainty each year on the allocation.

“Of course, if the UK is outside the EU, it will have their own fisheries policy and they will be an independent coastal state, and everything will not remain the same,” he said.

“But the real issue with fisheries is where can you fish, and how much. And with these two things, it is easy: we have the quota sharing set in stone. And we want an agreement that reflects what we have now.

“You can ask whether that is realistic, but the UK points to Norway. With Norway, the quotas are set in stone. There is an allocation key from the early 1980s. And that hasn’t changed.”

An EU source said: “In reality, if we can’t agree on fish then we really are in trouble.”

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