THERESA May has agreed to pay France £44.5million to beef up French border security at Channel ports following talks with Emmanuel Macron today.
The Prime Minister insisted the updated immigration agreement would "work in the best interests of both France and the UK".
UK officials said the cash would go towards high-tech kit such as carbon dioxide monitors and heartbeat monitors to find stowaways hidden in vehicles bound for Britain.
The money will also be spent on more traditional security measures like fencing and new CCTV systems to prevent ports like Calais becoming what Mr Macron has branded a "back door to Britain".
Part of the sum will go towards relocating people away from Channel ports in an attempt to stop another migrant camp like the "Jungle" from forming as it did in Calais in 2015.
The commitment forms part of an updated immigration treaty agreed between Mrs May and Mr Macron known as the Le Touquet agreement.
The treaty allows Britain to carry out its border checks on the French side of the Channel but has come under fierce criticism in France because some argue the deal is unfairly weighted in the UK's favour.
Announcing the agreement at the Royal Military Academy Sandhurst, this evening, Mrs May said the UK and France “remain committed” to the principles of the treaty.
She said: “Today we have agreed additional measures which will work in the best interests of both France and the UK, increasing the effectiveness of our cooperation.”
The French President has been in talks with Mrs May throughout the day during his first visit to the UK since becoming president in May last year.
The UK has already stumped up more than £100million for additional security in Calais over the last three years.
But the investment has seen the number of people attempting to enter Britain illegally fall dramatically, from some 80,000 in 2015 to just over 30,000 last year.
However, Mrs May’s decision to cave into French demands has already been poorly received by some of those in her own party.
Even before the treaty was formally agreed this afternoon, Tory MPs were criticising the PM.
Christopher Chope, a Conservative member of the Commons home affairs committee, said: “We keep handing over money for security and France keeps coming back for more. Enough is enough.
“They keep holding us to ransom. It has been suggested that this is a price we need to pay for a trade deal with the EU but it certainly raises a lot of questions.”
Andrew Bridgen, Tory MP for North West Leicestershire, said: “We should send the bill to Angela Merkel, who invited the world into a borderless Europe.”
And as part of their agreement, Britain could also commit to taking more child refugees from France as part of its commitment to resettle 480 unaccompanied children under the Dubs scheme, the Press Association has reported.