Britain will commit to spending £44.5 million (Dh226mn) to strengthen border controls in France at a summit meeting on Thursday between premier Theresa May and French president Emmanuel Macron.
The French city of Calais emerged as a hotspot during the European migration crisis with thousands of people gathering near the northern port before a final attempt to reach Britain.
Under pressure from Britain, France razed the so-called ‘Jungle’ – a squalid mass encampment of some 10,000 people – near Calais in 2016.
Mr Macron visited the city on Tuesday where he vowed there would be no return to such mass encampments, but hundreds of people remain camped out in scrubby woodland close to the port.
Rights groups have claimed that migrants face continuous harassment from French law enforcement, including the tearing up of makeshift camps, seizure of clothes and the use of incapacitant spray to deter migrants from heading to the northern coast.
The deal to increase security was viewed as a climbdown by Britain in the face of French demands by Eurosceptic sections of the UK media. A headline in the Daily Mail described the deal as "Le Stitch-Up" in a front-page headline.
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The money will be spent on fencing, security cameras and other technology to prevent migrants stowing away on lorries to try to reach Britain.
"That border is one of the most secure in Europe," Britain's ambassador to France, Ed Llewellyn told the BBC. He said there are now around 500 migrants in the Calais area.
UK funding for security in the region is thought to have topped £100 million over the last three years, while more than 750 children have been transferred to Britain since the Jungle was shut down. Mr Macron is reportedly pushing for a commitment to take more refugees.
A Government spokeswoman said: "This is about investing in and enhancing the security of the UK border.
"Just as we invest in our borders around the rest of the UK, it is only right that we constantly monitor whether there is more we can be doing at the UK border controls in France and Belgium to ensure they are as secure as possible."
Mr Macron and Mrs May were due to meet at the Sandhurst military academy on Thursday, in a sign of the two leaders' determination to retain close military and intelligence ties despite the UK's decision to leave the European Union.
The heads of the country’s intelligence agencies were due to discuss ways they could work together to counter terrorist threats.
"Today's summit will underline that we remain committed to defending our people and upholding our values as liberal democracies in the face of any threat, whether at home or abroad," said Mrs May,
President Macron is one of main flag wavers for a closely-integrated Europe and will be a key figure as the UK negotiates the terms of its departure and the likely shape of any future relationship.
Britain will also commit to participating in Mr Macron's 'European intervention initiative', which officials do not regard as a European army but a plan to enhance co-ordination of existing armed forces.
Britain's three RAF Chinook helicopters and around 50 non-combat troops will be deployed to Mali to provide logistical support to French forces attempting to stabilise the Sahel region of Africa where Islamist extremists have gained a foothold.