- The UK government hopes to use the summit to boost UK-French efforts to stop migrants crossing the English Channel.
- But the two countries are not expected to reach a deal on returning migrants arriving in the UK to France.
Spending more money with France to stop small boat crossings is a "sensible investment", Rishi Sunak has said during an Anglo-French summit in Paris.
The PM has met French President Emmanuel Macron and the two men are holding a news conference later.
Speaking ahead of their meeting, Mr Sunak said giving France £63m a year to boost policing on its beaches was yielding benefits for the UK.
He argued it was better than paying to house migrants in the UK.
"I think everyone knows that we are spending £5.5m a day plus on hotels - we would rather not do that, and the best way to stop that is to stop people coming in the first place," he said.
The UK government hopes to use the summit to boost UK-French efforts to stop migrants crossing the English Channel.
But the two countries are not expected to reach a deal on returning migrants arriving in the UK to France.
The French government is thought to prefer a deal between the UK and the European Union, something of a frustration to British diplomats who would like to see quicker action.
"We want a EU-UK returns agreement and will push that forward," the prime minister's spokesman said.
"But it is equally important that there is work on the ground right now to stop the crossings we are seeing even in these winter months."
A French government source said: "At this stage, and due to Brexit, there is no readmission agreement between France and the United Kingdom."
Labour said the absence of a new agreement to return migrants to France was a "total failure".
The conflict in Ukraine, nuclear power and renewable energy are also on the agenda for the summit.
Mr Sunak also said he was planning to talk to the French president about relations with China, ahead of Mr Macron's visit to the country.
The prime minister met Mr Macron at the Elysee Palace on Friday morning and the two men are now taking part in a roundtable discussion with French and British companies.
Mr Sunak is being accompanied on his trip by Foreign Secretary James Cleverly, Home Secretary Suella Braverman and Environment Secretary Therese Coffey.
The summit comes in the week Mr Sunak unveiled his plans to deter people from making the channel crossing in small boats.
Under the plans, anyone found to have entered the UK illegally would not only be removed within 28 days, but also be blocked from returning or claiming British citizenship in future.
Those arriving on the UK's beaches would either be returned to their home country, or another "safe third country" like Rwanda.
The British government feels the relationship with their opposite numbers in Paris on this issue has improved significantly in the last couple of years.
But Downing Street's desire "to make the small boat route across the Channel unviable" is a bold ambition - especially given that the numbers proving it to be the opposite have continued to rocket.
More than 45,000 people entered the UK via Channel crossings last year, up from about 300 in 2018.
So far this year, around 3,000 people have arrived on small boats, but the two governments claim their joint work has stopped a similar number from embarking on the journey.
An announcement on deepening co-operation on the issue is expected, rather than a big breakthrough.
The joint work the two countries do on this issue remains politically sensitive, as our Europe editor Katya Adler writes here.
Officials point out that both the UK and France are nuclear powers, members of the G7, G20 and the Nato defence alliance and permanent members of the United Nations Security Council.
Brexit has been something of a stone in the shoe of the relationship between the UK and France in recent years.
But diplomats believe the deal between the UK and the European Union on Brexit arrangements in Northern Ireland creates a much better atmosphere between the two countries.
It is a month of particularly intense activity between the two countries - as King Charles and the Queen Consort will be in France in a few weeks.
Next year marks the 120th anniversary of the Entente Cordiale, which put an end to centuries of rivalry between the two countries.