Britain is to boost its contribution towards security at border controls in France by tens of millions of pounds.
Ministers will announce the £44.5 million cash injection as Theresa May meets French President Emmanuel Macron in a high-profile summit on Thursday.
The Government said the extra money will go towards fencing, CCTV and detection technology in Calais and other ports along the Channel.
Reports emerged earlier this week that France wanted to secure a rise in Britain's financial contribution, as well as a commitment to take more refugees.
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" camp was shut down.
Officials said the new funding builds on previous security work in the area, pointing to figures showing illegal attempts to enter the UK fell from more than 80,000 in 2015 to just over 30,000 last year.
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."
Up to 7,000 men, women and children lived in the Jungle in Calais before the site was cleared in 2016.
But hundreds of asylum seekers hoping to cross the Channel remain in the area, more than a year after authorities dismantled the sprawling site.
Officials said the new funding will also help relocate migrants away from Channel ports to stop another similar camp forming.
The Government emphasised that the UK plays an "important role" in the worldwide effort to tackle the migration crisis, providing hundreds of millions of pounds in aid and resettling children and vulnerable people from refugee camps around Syria and Europe.
"But President Macron is right when he said earlier this week that those people already in France and in need of asylum should seek help there," the spokeswoman added.
"The French are working hard to make sure people are treated fairly and given the support they need.
"Attempting to cross the Channel illegally is dangerous and not a journey which people should try to make."
Thursday's summit has prompted fresh scrutiny of the accord known as the Treaty of Le Touquet.
Signed in 2003, the bilateral agreement allows British immigration officers to check passports in Calais, while their French counterparts do the same in Dover - a system referred to as "juxtaposed controls".