Sir Keir Starmer has accused Home Secretary Priti Patel of failing to deliver on promises to stem the flow of illegal migrants crossing the Channel.
The Labour leader said Ms Patel has not secured strong enough agreements with the French government to prevent migrants making the dangerous sea journey.
He said the Home Secretary repeatedly used “strong language” to say how she would tackle the problem but delivered “absolutely nothing”.
His attack came as Ms Patel blamed the EU’s open borders – established by the Schengen Agreement – for failing to check the movement of people through the bloc.
Speaking to reporters during a visit to Washington, she said she was “constantly pressing” the French on the issue but that they were “overwhelmed”.
“Let’s not forget that the real problem on illegal migration flows is the EU has no border protections whatsoever – Schengen open borders,” she was quoted as saying.
More than 24,700 people have arrived in the UK so far this year after making the Channel crossing in small boats – almost three times the number there were in 2020.
This includes at least 1,247 who arrived since Monday, according to data compiled by the PA news agency. This number is set to rise as the exact figure for Tuesday is still being finalised by the Home Office.
It is thought at least 10 migrants have died in the last few weeks while trying to make the dangerous crossing.
It comes as campaigners threatened the Home Secretary with legal action over so-called pushbacks after reports she had sanctioned the tactics to turn migrants around back towards France at sea.
Meanwhile, French President Emmanuel Macron is reported to have said the British “oscillate between partnership and provocation” when discussing the migrant crisis in an interview with Lille-based newspaper la Voix du Nord, adding: “We need to further strengthen collaboration.”
Officials have described how violence levelled at French police has intensified recently, highlighting incidents where an officer had their ear bitten off, and another where cannisters of CS gas had to be used to disperse a group of migrants.