The prime minister has sought to soothe relations between France and the UK, telling journalists en route to the G20 in Rome that France is one of the UK’s “best, oldest, closest friends and allies”.

Asked what he would say to President Macron when the pair meet in Rome this weekend, Mr Johnson responded: “[The] ties that unite us, that bind us together, are far stronger than the turbulence that currently exists in the relationship.

“That is what I will say to Emmanuel, who has been a friend for many years.

“And what I will also say is that there may be people on either side of the Channel that they think they have an interest in promoting disharmony between the UK and France and creating the impression of disharmony. I don’t think Emmanuel shares that perspective.”

On the issue of retaliation, the prime minister said he was “puzzled about what was going on, and we fear there may be a breach of the trade and cooperation agreement” and “we will stand by to take the appropriate action”.

Asked if the UK would back down on fishing licences, the PM said “we will do whatever is necessary to ensure UK interests”.

Mr Johnson said he would be “surprised” if the French snarled up trade across the Channel.

“I haven’t heard that from our French friends, I would be surprised if they adopted that approach.”

The PM told reporters that UK fishermen should be confident in going about their lawful business, wherever that will be.