France would cease keeping migrants in Calais and tempt bankers to relocate from Britain if the country exits the European
Union, economy minister Emmanuel Macron told the Financial Times.
The comments come before Prime Minister David Cameron and President Francois Hollande are due to meet at an Anglo-French summit, with Britain's June referendum on whether to remain in the European Union high on the agenda.
Macron told the newspaper that a so-called Brexit could scupper an agreement between the two countries that allows Britain to conduct border controls on the French side of the border, and that Paris could seek to lure financial services to relocate from London.
“The day this relationship unravels, migrants will no longer be in Calais and the financial passport would work less well,” Macron told the newspaper, adding that Britain would no longer have full access to the single market once outside the EU.
"People deciding to leave the single market will not be able to secure the same terms,” he said.
And echoing Cameron's famous offer that the UK would roll out the red carpet to French businessmen wanting to quit France over high taxes Macron warned: “If I were to reason like those who roll out red carpets, I would say we might have some repatriations from the City of London.”
Cameron warned last month that Brexit could mean British border checks being removed from Calais and that "there would be nothing to stop thousands of people crossing the Channel overnight".
But pro-Brexit campaigners accused Cameron of scaremongering and some experts said it's unlikely to happen given that France would not only miss out on British funds to help pay for the crisis, but they also fear many more migrants would come if they thought it was easier to get to the UK.
Last October France's Interior Minister Bernard Cazeneuve said: "Calling for the border with the English to be opened is not a responsible solution.
"It would a send a signal to people smugglers and would lead migrants to flow to Calais in far greater numbers. A humanitarian disaster would ensue. It's a foolhardy path and one the government will not pursue."
"Despite the growing opposition and anger in France and the fears in Britain of Paris taking advantage of any Brexit it seems the British border police are in France for the foreseeable future."
The French government and president Hollande has repeatedly said that they want the UK to remain in the EU while warning that a Brexit would be bad for both Britain and Europe.
However some have suggested a Brexit would present France with a "tremendous opportunity".
"A Brexit would represent a historic windfall for the city of Paris," said French essayist Edouard Tétreau.
"In a few months the City of London will lose the essence of its raison d'être – to be the financial hub of Europe.
"But when it's transformed into an offshore (literally) fiscal paradise the City of London would force away all the banks and asset management funds who want to continue to operate in the European market, without the barriers caused by regulations and taxes that would be applied to London-based institutions once they are outside the Union.
"Thousands of managers, lawyers, financiers, and also the heads of the European subsidiaries of multi-national companies would have to leave the UK to remain within the EU to continue their work."