Brexit ping-pong as both sides say 'ball in your court'

May, meanwhile, said in a speech on Monday to MPs in the Westminster parliament that "the ball is in their [EU] court".

"Achieving that partnership will require leadership and flexibility, not just from us but from our friends, the 27 nations of the EU," she said.

This latest war of words comes as the fifth round of Brexit talks started on Monday in Brussels.

May was hoping to get the green light to start talks on a 'transition period' later in October, when EU leaders gather in Brussels for a summit.

The British prime minister's weak domestic political position could be strengthened if she would get some sort of political concession from Brussels, as four rounds of negotiations have so far failed to bring any breakthrough on the key issues of a financial settlement, citizens' rights and the border in Ireland.

"[…] We should concentrate our negotiating time and capital on what really matters – the future long-term relationship we will have with the EU after this temporary period ends," May told MPs on Monday evening.

Starting the second phase of negotiations on trade can come only if EU leaders agree that there has been "sufficient progress" made in the Brexit negotiations, but that is unlikely to happen at the October summit and will be dealt with again in December.

The British PM was hoping for a move on the transition period at least.

May was meeting British business leaders on Monday, who are increasingly concerned over the slow pace of Brexit talks, and need to make decisions on moving headquarters or rearrange their businesses if the UK in effect leaves the bloc and its internal market on 31 March 2019.

No talk of money

However heavy-weight member states link any willingness to talk about a transition period of possibly two years after 2019 to having more clarity on the financial deal with the UK.

At a meeting of EU ambassadors last Friday, reported by the Financial Times, Germany and France opposed the idea - which Brexit negotiator Michel Barnier argued could break the negotiating impasse.

May said in her keynote speech in Florence last month that the UK would honour its financial commitments.

But the UK's strategy is to basically isolate talks on a financial settlement, and link it to the framework of a future trading relationship.

"[…] This can only be resolved as part of the settlement of all the issues that we are working through," May said on Monday.

"They see the payment as their leverage to negotiate access to the single market and other benefits the EU has," an EU source said.

UK negotiators will not outline in further detail this week what May meant by her pledges on a financial settlement in Florence - only technical consultations are expected to take place.

So far the UK has committed to paying into the EU's seven-year budget in 2019 and 2020, when the budget officially runs out. However, some payments could continue until 2023.

A source said that opposition to opening talks on transition is a way of putting increased pressure on London. "Some would ask for a higher price," another EU source said earlier.

The opposition could also stem from countries competing for UK-based companies looking for a new base on the continent, and from wanting to maintain the integrity of the single market, the first source added.

But it is not all about the money. EU countries don't want to undermine their own timeline either by starting transition talks before the first phase of discussions end.

Talks on citizens' rights on the other hand are progressing, with the UK hoping to reach further results on that streak this week.