Calais migrants
Migrants trying to reach the Channel Tunnel laugh as they run past policemen in Coquelles near CalaisPhilippe Huguen/AFP

The Union for Borders, Immigration & Customs (ISU) has painted a rather stark picture of what would happen if Britain's border checks in Calais are scrapped. Some French politicians are threatening to end the Le Touquet agreement signed between the UK and France in 2002 which paved the way for border controls to be carried out at Calais rather on British soil.

The Le Touquet deal is said to have dramatically cut illegal immigration across the channel.

Lucy Moreton, the General Secretary of the ISU union which represents officers from the UK Border Force, Immigration Service and HM Revenue and Customers, told the Daily Mail that she believes the end of the Le Touquet deal would effectively mean the return to the illegal immigration chaos seen in the 2000s when the number of migrants seeking asylum hit 84,132 a year.

Tens of thousands of illegal immigrants could land in Dover if the border controls in Calais are moved back to Britain, the union said. Moreton added that the UK authorities would be powerless to return the hundreds of stowaways caught every day trying to sneak aboard ferries to Britain.

Last year alone, UK Border guards thwarted 30,629 attempts by immigrants to illegally enter the UK between April and July- an annual rate of 92,000, according to Home Office figures.

"This means that hundreds of irregular migrants detected every day whilst still in France but attempting to reach the UK who are currently simply returned to the French authorities would have arrived in the UK and would have to be processed here," said Moreton.

"Although applications for entry may be ultimately unsuccessful this can be a lengthy process putting strains on the detention estate, as well as pressures on the benefits and other support systems, " she added.

Damian Collins, MP for Folkestone and Hythe said the threat must be taken seriously as Britain cannot accept 'the illegal immigration of the past.' He added: "We cannot allow the situation in Calais to occur in the UK."

A UKIP councillor for Dover District Council, Andrew Richardson warned: "The scrapping of the Le Touquet agreement could well be carnage for Dover and Folkestone. The French cannot simply open the flood gates and let the thousands of migrants waiting in Calais to walk through the Channel Tunnel."

Richardson added: "This is a potentially catastrophic result of the Brexit vote. If a jungle-style migrant camp were to open in Dover, UKIP would have to share some of the responsibility for it happening because we have called for Britain to leave the EU."

He however pointed out that the French had been calling for the scrapping of the agreement "long before the Brexit vote. "So this problem could have arisen whether we were in the EU or not. The existence of a migrant camp on either side of the channel - in Calais or Dover - shows that we have failed to deal with this problem effectively."

Alain Juppe, the current favourite in the next French presidency race is one of the politicians seeking to have the Le Touquet deal scrapped. He has said that it was logical for these checks to take place in the UK now that Britain is leaving the European Union.