The country's finance minister says it will "roll out the red carpet" for firms who want to leave Britain if it is outside of the Single Market
The Calais "jungle" refugee camp could be relocated to Britain if the UK chooses to leave the European Union, according to France's economy minister.
In an interview with the Financial Times, Emmanuel Macron warned that Brexit would threaten the bilateral relationship between the UK and France.
He said the Le Touquet Agreement, which allows British authorities to conduct border checks on the French side of the Channel, thereby keeping illegal migrants out, could be scuppered if the UK decides leaves the EU.
"The day this relationship unravels, migrants will no longer be in Calais and the financial passport would work less well," Mr Macron said.
The newspaper also reported that Mr Macron believes many financial services workers will leave London for France once their institutions lose the "passport" rights to work across the EU.
"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," Mr Macron said.
The comments come ahead of an Anglo-French summit in Amiens today attended by Prime Minister David Cameron and President Francois Hollande.
The two leaders are expected to announce £1.5bn of investment in a joint project to build the next generation of unmanned military drones.
They will also discuss how the two countries can work together to fight terrorism in Europe.
Mr Macron's comments echo sentiments expressed by Downing Street last month when it claimed the Calais camp could move to England's south overnight if Britain leaves the EU.
Eurosceptics accused Number 10 of "scaremongering over immigration" at the time.
Demolition teams and riot officers moved into the Calais camp this week to clear migrants, refugees and activists from the site.
French authorities have been determined to halve the size of the sprawling, squalid makeshift settlement, which has been home to thousands of people - mostly from Africa, Afghanistan and the Middle East.