France's former prime minister and presidential favourite Alain Juppe has called for the UK border to be shifted across the Channel from Calais, in an interview published on Thursday.
Opinion polls suggest Juppe is leading the race to be the right-wing candidate in next year's presidential election and as a result is the favourite to be elected to the Elysée given the unpopularity of President François Hollande.
If he wins next May, one of his first phone calls is likely to a difficult one to British Prime Minister Theresa May.
"We can't tolerate what is going on in Calais, the image is disastrous for our country and there are also extremely serious economic and security consequences for the people of Calais," Juppe told journalists.
"So the first thing is to denounce the Le Touquet accords," he added, referring to the 2003 agreement which extends the UK border to Calais' ferry ports. Under the deal British officials check passports and inspect vehicles.
"We cannot accept making the selection on French territory of people that Britain does or doesn't want. It's up to Britain to do that job," he said.
Juppe, 71, said "of course" the border should be moved back to the UK in spite of British opposition. "Don't tell me it's difficult because the British don't want it."
"So the debate must be opened and a new accord obtained with Britain," he said.
The politician's comments followed the French government's announcement on Tuesday that the "Jungle" migrant camp in Calais, where thousands of migrants have gathered in the hope of reaching Britain, would be demolished imminently.
French Interior Minister Bernard Cazeneuve told parliament that talks with London to see Britain take in some of the hundreds of unaccompanied minors were "proceeding very smoothly".
The first group of 14 teenagers arrived in Britain on Monday.
Cazeneuve said those remaining at the site, which currently hosts around 5,700 people according to official figures, would be given "dignified" shelter.
French Foreign Minister Jean-Marc Ayrault in June warned against dismantling the Le Touquet agreement, saying it could prompt people to try to cross the Channel.
"If the border is moved to the other side of the Channel, as some suggest, we'll have to put out boats to rescue people who will be in the water," Ayrault told AFP.
As a bilateral deal the Le Touquet agreement is not dependent on the European Union, although Britain's decision in June to leave the EU has brought immigration controls under the spotlight.
Juppe said he respected the outcome of the UK referendum and called for Brexit to be implemented quickly.
"It's not about punishing Britain, it's about being coherent," he said, while asserting that France would maintain "very close bilateral cooperation with the UK" on matters such as defence.