David Frost, the UK’s chief negotiator on a post-Brexit trade deal on Sunday (6 September) upped the ante ahead of a crunch week of negotiations, warning that Boris Johnson’s government was not “scared” of walking away from talks without a deal to govern trade from 2021.

Frost will host EU counterpart Michel Barnier for the eighth round of talks in London, starting on Tuesday, with both sides under pressure to break a lengthy log-jam on regulatory alignment and fisheries.

In an interview with the Mail on Sunday, Frost also pinned the blame for the impasse on the team of Boris Johnson’s predecessor as Prime Minister, Theresa May, who he said had “blinked and had its bluff called at critical moments” during negotiations on the Withdrawal Agreement that took the UK out of the EU this January.

As a consequence, Frost said that the EU had “learned not to take our word seriously”.

That prompted an angry reaction from Gavin Barwell, chief of staff for May, who accused Frost of “brass neck”, pointing out that 95% of the Withdrawal Agreement signed off by Johnson was negotiated by May.

“The 5% that was new involved giving in to the EU’s key demand,” said Barwell, a reference to Johnson agreeing to the EU’s ‘backstop’ proposal to avoid a hard border between Northern Ireland and the Republic of Ireland.

Although the post-Brexit transition period ends on 31 December, the window for agreeing a new trade pact with sufficient time for it to be ratified by national parliaments and the European Parliament is steadily closing.

In a BBC interview on Sunday, Foreign Secretary Dominic Raab also sought to put the pressure on Barnier, warning that this week’s round would be “a wake-up call for the EU” and repeated that a deal was “there for the taking” if the two sides could broker a compromise on state aid and fisheries.

Fisheries appears to be tougher to resolve. The EU has demanded fishing arrangements that gives EU trawlers access to UK waters comparable to that offered by the Common Fisheries Policy, while the UK wants the EU’s 40 year old fisheries agreement with Norway to be the model for its own settlement.

Boris Johnson’s government is expected to outline its plans for the UK’s future state aid regime later this month, a move which officials hope could pave the way to a compromise. Barnier has stated that the EU cannot agree to a trade deal without knowing what the UK’s subsidy regime will look like, though Barnier’s team have indicated that this does not mean that the UK must necessarily mirror EU state aid rules.

“I think this week is an important moment for the EU to really effectively recognise that those two points of principle are not something we can just haggle away,” said Raab.

The two sides’ positions have hardened in recent weeks. Last week, Barnier said that he was ‘worried and disappointed’ by the UK’s refusal to offer compromises, while French foreign minister Jean-Yves Le Drian blamed the lack of progress on “the UK’s uncompromising and, to be frank, unrealistic attitude”.