Sir Keir Starmer said the UK would tackle illegal migration with “new tactics” and a “new level of intent” before crunch talks to hammer out a deal with Emmanuel Macron.
The French president said the UK and France “share the same will” to address the issue at the start of a Franco-British summit at Downing Street.
It came after the pair said a “new deterrent” was needed to stop small boats crossing the English Channel.
The Prime Minister hopes the French president will sign up to a “one in, one out” deal on Thursday, the last day of Mr Macron’s state visit to the UK.
Under the terms of the deal, Britain would accept migrants with links to the country in exchange for sending others back across the Channel.
Sir Keir said the meeting was about working together on shared priorities.
He said: “For us, it’s about delivering the changes that the British people want to see, and we will agree the situation in the Channel cannot go on as it is.
“So we’re bringing new tactics into play and a new level of intent to tackle illegal migration and break the business model of the criminal gangs.”
Speaking in French, Mr Macron said: “We share the same will to tackle networks of illegal immigration through great co-ordination with other European countries.
“We have often mentioned France is the last destination before Great Britain for these men and women who often journey through paths of misery and are exploited by traffickers.
“We will work with countries of first entry in Europe (as) our intention is also to engage all countries who share a responsibility alongside us.”
Home Secretary Yvette Cooper, Chancellor Rachel Reeves and Energy Secretary Ed Miliband were also at the summit.
Defence Secretary John Healey, who was also at the summit, told ITV’s Good Morning Britain that footage of French authorities puncturing a migrant dinghy to stop it from setting off last week was a “recognition” that France has agreed to change its rules to intervene in shallow waters.
To reduce small boat crossings, he said those changes need to be “fully implemented” alongside new legislation, building up the new border security command, and any steps to be announced by Sir Keir and Mr Macron after the summit.
French newspaper Le Monde has reported that some 50 migrants a week would initially be returned to France under the terms of the proposed deal, which it described as largely symbolic.
If such a deal were struck, it would only result in the return of a fraction of the 21,000 people who have made the Channel crossing so far in 2025, a record for this point in a year.
But it would also represent a concession by the French that such returns are possible, after years of MPs on the right of British politics insisting France is a “safe” country where migrants can be sent back to.
The Times reported the scheme would be scaled up after an initial pilot had shown “proof of concept”, citing Government sources.
In return, Mr Macron is said to be pushing for the UK to do more to address “pull factors” which are attracting people to make the dangerous crossing to the English coast.
When Mr Macron and Sir Keir met in Downing Street on Wednesday, the small boats crisis appeared to be the mainstay of their conversations.
The pair agreed the crossings are a “shared priority that requires shared solutions”, a Downing Street spokesperson said.
They also agreed on the need for a “new deterrent to break the business model of these gangs” and are aiming for “concrete progress” on the matter.
Following the French-UK summit, the two leaders will host a call with coalition of the willing partners, the proposed peacekeeping mission to deter Russia from attacking Ukraine in future.
In a sign of close alignment on defence, Britain and France have announced they will buy new supplies of Storm Shadow missiles, which both have loaned to Ukraine to strike targets deep inside Russia.
The two nations will also work closely to develop a successor to the long-range missile, the Ministry of Defence said.
