Asked whether he thought EU insistence that the European Court of Justice (ECJ) oversees a citizens' rights deal could force the United Kingdom to quit the negotiations, Mr Barnier said: "Quite frankly, it is not really in my nature, or in my philosophy, to try and push our partners across the table to the edge, particularly not on this specific topic of citizens' rights".
"I'm not hearing any whistling, just a clock ticking", Michel Barnier told reporters on Tuesday in Brussels after an Irish Times reporter referred to Johnson's remarks. We can not remain idle as the clock is ticking'.
Mr Barnier is to be congratulated on his little bon mot - the man knows how to deliver a line - but that doesn't mean his version.
Briefing journalists after reporting to the European Commission on the talks so far, Mr Barnier refused to be drawn directly on United Kingdom foreign secretary Boris Johnson's jibe on Tuesday that the EU could "go whistle" for the alleged €100 billion exit payment being demanded of the United Kingdom, beyond saying he could hear "no whistling, just a clock ticking".
Johnson added that no contingency plan is in place in case the United Kingdom crashes out of the European Union, as he claimed the country will get a "great deal" in its Brexit negotiations.
However, he insisted that there must be progress on all three divorce issues before moving onto trade talks, adding that "progress on one or two would not be sufficient".
In some of the most strident exchanges of the Brexit process so far, Barnier said the issue was not simply a technical sequencing matter but went to the heart of whether the two sides could trust each other.
He told reporters that: "Trust means [the UK] settling its accounts". It's not easy and it might be expensive, but we are not asking for a single pound or euro more than they have legally agreed to provide.
Last month, Davis caved in to the EU's demand for citizens' rights, the size of Britain's "divorce bill" and border issues to be settled at the outset of the negotiations.
Barnier observed, as he has previously, that the best option for the United Kingdom would be to remain in the EU, but he suggested that a second-best alternative would be to remain a member of the European Economic Area in an arrangement similar to those of Norway and Liechtenstein.
This position was praised by Chuka Umunna, the Labour MP and former shadow business secretary, who said it was a "bold and important" move for Cortes to say Labour should forget single market membership and now argue to stay in the EU.
Speaking the day after Brexit secretary David Davis gave MPs an update of negotiations, Barnier said he was seeking clarification on a number of British positions, saying his team could begin to act as soon as they received them.
Before meeting Davis on Monday, Barnier will hold talks with both Jeremy Corbyn and Nicola Sturgeon and Carwyn Jones, the leaders of Scotland and Wales respectively.
Other European countries are highly unlikely to follow Britain's example in leaving the EU, Britain's Brexit secretary acknowledged yesterday.