An extra £44.5m is to be spent beefing up Channel border security, the UK government is to say later.
It will be spent on fencing, CCTV and infrared detection technology in Calais and other border points.
It comes as French President Emmanuel Macron visits the UK for a summit with Theresa May.
Britain is also expected to commit to taking more migrants from Calais, especially unaccompanied children, the BBC’s James Robbins said.
He added that while Britain and France were heading in different directions as a result of Brexit, both governments are keen to show that they will continue to work closely together.
Other commitments being unveiled include the deployment of three RAF Chinook helicopters in Mali, where French forces are fighting Islamic extremists, and France sending more troops to reinforce a British contingent in Estonia on Nato’s border with Russia.
On what will be his first visit to the UK as president, Mr Macron is also expected to announce the loan of the Bayeux Tapestry for display in the UK.
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Thursday’s summit has prompted fresh scrutiny of the border arrangements between France and the UK.
During last year’s French election campaign, Mr Macron said he wanted to renegotiate or scrap the 2003 Le Touquet agreement, which established French border controls in Britain and UK controls in Calais.
The agreement means undocumented migrants barred from entering the UK stay in France – many in makeshift camps.
Up to 700 migrants are in the area, despite the camp known as the “Jungle” having been dismantled in 2016.
The UK government is already thought to have spent over £100m on security in the area over the last three years, and officials said the number of illegal attempts to enter the UK fell from 80,000 in 2015 to just over 30,000 last year.
A government spokeswoman said the latest investment was “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.”
Other “juxtaposed” border controls are in operation at Eurostar stations in France and Belgium.
The summit between Mrs May and Mr Macron, at the Royal Military Academy Sandhurst in Berkshire, will also feature the first meeting of the heads of Britain and France’s five intelligence agencies, and will be attended by UK cabinet ministers and their French counterparts.
Downing Street said the RAF Chinooks would offer a “niche capability”, providing logistical support for the French operation in Mali, but that Britain would not be committing combat troops.
Speaking ahead of the summit, Mrs May said: “Today’s summit will underline that we remain committed to defending our people and upholding our values as liberal democracies in the face of any threat, whether at home or abroad.
“But our friendship has always gone far beyond defence and security and the scope of today’s discussions represents its broad and unique nature.”
UK pledges extra £44m for Channel border security}