The Prime Minister used the architectural term, for an external arch that supports a building such as a church, while addressing UK embassy staff in Paris ahead of lunch with the French President.
Downing Street officials travelling with him were hopeful that Mr Macron will echo German Chancellor Angela Merkel and allow him a 30-day window to explain his Brexit plans before deciding if there is no deal to be done.
But the signs were not good. Allies of Mr Macron said there could be no renegotiation of Theresa May’s thrice-rejected withdrawal agreement and that it was time for the UK to “take it or leave it”.
“Mr Macron is going to be polite but firm,” said Bruno Bonnell, an MP in the President’s En Marche! party. “We are fed up with it. There is a time to put your stick in the ground and say ‘take it or leave it’.”
This morning Mr Johnson had a working breakfast at the Paris embassy with the UK ambassador before telling diplomats: “The UK would be a flying buttress for Europe.”
British officials felt that reporting was “overblown” of last night’s meeting with Mrs Merkel in Berlin, especially the notion that she had given a major concession when she told him to come up with concrete ideas within 30 days for how a hard border with Ireland could be avoided.
“It’s good she wants to talk but we aren’t reading too much into this,” a No 10 official said.
The official said the dinner with Mrs Merkel was “warm and constructive” and wide-ranging, but stressed: “Past governments have put far too much faith in Merkel for a decade and we have no illusions.”
Politically, however, Mrs Merkel might have thrown a lifeline to Mr Johnson as he could use the prospect of talks in 30 days to deflect demands for a no-confidence vote in his Government.
And the hope was that Mr Macron would follow Mrs Merkel’s lead by softening his language on Brexit.
“Merkel made clear there is an opportunity to talk, so we assume Brussels and France will want to do the same,” said an official.
However, Mr Macron was disparaging about Mr Johnson’s Brexit plans in a briefing with French journalists yesterday, saying that Britain would be “the main victim” and would end up dependent on the US.
He said: “And even if it were a strategic choice it would be at the cost of a historic vassalisation of Britain.
“I don’t think it’s the will of the British people … to become the junior partner of the US.” French MP Pierre-Henri Dumont told BBC Radio 4’s Today programme: “We are very fed up about Brexit right now in France and Europe. The question now is … to take the deal or not. There is actually no other solution than the deal and I don’t see any chance to reopen negotiations.”
He accused Mr Johnson of “pretending he has other options when there are none” and claimed the purported benefits of a no-deal Brexit “is a total lie to the UK people”. He added: “We see that it is going to be disaster.”
Former Brexit secretary David Davis claimed Mrs Merkel’s softer approach reflected “regret” that she had allowed the backstop issue to dominate. “I certainly expected him to come away with a flea in his ear,” he added.
Jeremy Corbyn today promised to do “everything necessary” to stop what he called a “no-deal carnage”.
The Labour leader was due to visit a farm in Keswick to investigate claims that millions of lambs will be slaughtered if food sales are disrupted.
Mr Corbyn last night invited leaders of other parties and senior backbenchers from across Parliament to meet urgently to discuss tactics available to prevent a no-deal Brexit.