France and Britain plan to announce Thursday a new treaty on how to handle the thousands of migrants hoping to cross the English Channel from the northern French coast, as the two countries look to bolster relations as Brexit looms.

The new deal will "amend" the 2003 Le Touquet accord and which effectively put Britain's border on French soil at Calais, which has since become a sore point in relations between the two countries.

President Emmanuel Macron and British Prime Minister Theresa May will unveil the "new treaty" as the French leader makes his first official visit to London on Thursday for a summit meeting.

The details are "still being finalised", a source in the French presidency said Wednesday, but the deal will include measures on how to manage unaccompanied minors, asylum requests and family regroupings.

"Specific engagements" will also be announced to respond to asylum and other requests "within a few days", the source said, asking not to be named.

Britain will also commit to a "major" financial contribution as part of a "reinforcement of French-British police cooperation on border management", it said.

"Significant results have already been seen, including fewer asylum requests in Great Britain and an improvement in the situation on the ground on the French side," it added.

The original Le Touquet text, which came into force in February 2004, implemented joint controls at coastal ports in both countries as Britain, which is not part of Europe's Schengen visa-free zone, looked to bolster efforts to keep migrants out.

Later changes led to Britain financing some of the controls and security operations in Calais, just across the English Channel from its own port in Dover.

- Camps and stowaways -

Migrants hoping to stow away on trucks bound for Britain have long been drawn to France's northern coast, with the squalid "Jungle" camp near Calais once housing some 10,000 people before it was bulldozed by the government in late 2016.

Hundreds of migrants remain in the area, with police routinely breaking up makeshift camps of people hoping to head to Britain, a favoured destination for Afghans and east Africans.

French officials argue the Le Touquet deal has worsened Europe's migrant crisis by creating a huge backflow of migrants in the area, lured by a belief that it is easier to secure asylum and work permits in Britain.

A French human rights commission in 2015 said the accord had made France the "police branch" of Britain's immigration policies.

Macron made a renegotiation of the Le Touquet deal one of his campaign pledges, and Interior Minister Gerard Collomb signalled Tuesday that Paris would ask Britain to take in more refugees from northern France and increase its funding.

"It's in their interests that things go well," Collomb said.

In November, Collomb said there were about 300,000 undocumented migrants in France, and the government registered a record 100,000 asylum claims last year.

- Post-Brexit relationship -

The French-British summit, to be held at the Sandhurst Military Academy south of London, will also focus on a series of measures aimed at deepening military and intelligence cooperation, along with cooperation in other core matters such as climate change.

"The British have the same determination as us to say, 'Brexit is one thing, it's taking up all our energy, but the determination of both sides is to maintain, develop and cultivate this partnership" in terms of defence, a French government source said.

In particular the Sandhurst talks will cover missile and submarine detection programmes, as well as the Future Combat Air System, a joint two billion euro effort to build next-generation combat drones first agreed in 2016.

The two NATO allies also plan new initiatives within the framework of the trans-Atlantic defence treaty.

Such efforts stem from the historic 2010 Lancaster House accords signed by France and Britain, which are the biggest military powers in the European Union.

With economic pressures including inflation and the weaker pound crimping Britain's budget ambitions, "it's almost a great window of opportunity to deepen our cooperation," a French military source told AFP.

"In terms of defence, our road map remains the same regardless of Brexit, even if their resources will be more closely watched," the source added.

Britain is also expected to unveil Thursday that it will "significantly reinforce its operational support" for the west African "G5 Sahel" force aimed at fighting jihadism in the region.

Source: AFP