David Davis | Jack Taylor/Getty Images Brexit Files Insight David Davis, the UK’s Brexit attack dog Brexit secretary said to be ready to hit back at criticism from Brussels.

Just as Foreign Secretary Boris Johnson appeared to have found the dial-down button, replacing his “go whistle [for the money]” rhetoric with an insistence that Brits are “law-abiding, bill-paying people,” Brexit Secretary David Davis ended the summer in combative mood.

EU threats that Brexit talks will stall without clarity from the Brits on their financial obligations — the so-called Brexit bill — will be met with accusations from the Brexit secretary that Brussels is being “stubborn and unreasonable,” according to a government official quoted by the Sun.

Davis’ participation in the regular joint press conference with EU chief negotiator Michel Barnier at the end of the week could even be in doubt, the official said.

Pre-negotiation bluster is almost inevitable with leaders each playing to their home crowds, but with only one more negotiating round penciled in after next week before EU leaders will judge at the European Council whether “sufficient progress” has been made, time is not on the negotiators’ sides.

The U.K. is refusing to produce a methodology for the Brexit bill but prefers to critique the calculations put forward by their negotiating partners. “In an ideal world, they want to salami-slice us, step by step by step. And on you go, up and up, and there is the bill. That is not going to happen and we are not going to play that game,” said an official familiar with the U.K. negotiating position.

But despite the hard line on the bill, the official was optimistic the talks would move on to phase two in October, claiming they would be “staggered” if any of the separation issues became a serious stumbling block.

That optimism does not appear to be shared in Brussels. EU diplomats briefed by a senior member of Barnier's team at an all-day meeting on Thursday told POLITICO they are “increasingly doubtful” that the talks will move to the second phase of discussing trade in October.

On Wednesday, a research paper for Oxford Economics concluded that the chance of a successful separation and transition arrangement being agreed between Britain and the EU has fallen. And Charles Grant, the well-connected director of the Centre for European Reform, tweeted that while “greater than zero," the chances of the talks making sufficient progress by October are “small.”

With the two sides determined to hold their line on the Brexit bill next week, it will be a matter of who blinks first or whether a compromise can be found.

What's clear is that time in which to find a middle way is running out.

This insight is from POLITICO’s Brexit Files newsletter, a daily afternoon digest of the best coverage and analysis of Britain’s decision to leave the EU. Read today’s edition or subscribe here.