Theresa May is to hold talks with German chancellor Angela Merkel amid growing impatience among EU leaders at the UK's reluctance to spell out its goals in the Brexit negotiations.
The two leaders will meet in Berlin today (February 16) ahead of a speech by the Prime Minister in Munich tomorrow (February 17) on Britain's future security relations with the EU.
But with talks opening last week on the second phase of the Brexit negotiations, May is now facing demands from leaders of the remaining 27 member states to set out what sort of wider relationship she wants, including on trade.
Yesterday (February 15) a spokesman for Merkel said the British needed to come forward with concrete proposals, adding that "time is running out."
It followed reports she had mocked May's negotiating approach at last month's World Economic Forum at Davos, complaining every time she asked her want she wanted, the Prime Minister replied: "Make me an offer."
The latest German intervention echoed similar warnings from the EU's chief negotiator Michel Barnier, who said last week that a transition deal, which the Government is hoping to wrap up by the end of March, was "not a given."
He said there were "substantial" differences which had to be overcome if they were to agree transitional arrangements after the UK leaves in March 2019 to avoid the "cliff-edge" break which many businesses fear.
He also warned the return of border checks between Northern Ireland and the Republic was "unavoidable" if the UK pressed ahead with plans to leave the single market and the customs union, something ministers insist they do want to happen.
In setting out her negotiating aims, however, May has been constrained by the need to hold together her Government and her party, which remain bitterly divided over what kind of post-Brexit arrangements they want.
Many Tory Brexiteers remain angry at the EU's insistence that the UK must remain subject to EU law, including any new legislation passed after it leaves, during the transition period, expected to last around two years.
Feelings, which were already running high, were further inflamed when it emerged the EU was proposing a so-called "punishment clause", which could see it impose sanctions on the UK if there is any breach of the rules.
But after Bexit Secretary David Davis accused the European Commission of failing to act in "good faith", it was reported that officials from the other 27 states had agreed to tone down the language when they publish an expanded document towards the end of February.