Senior Labour figures have accused Rishi Sunak of a "desperate and pathetic" attack after he claimed the party was “on the same side” as criminal gangs trafficking people to the UK.
Shadow frontbencher Jim McMahon hit out at the prime minister, accusing him of getting in “the gutter”.
The furious row erupted just days after sources made clear Mr Sunak intended to launch a more aggressive political campaign around issues like immigration, on which the Conservatives see Labour as weak.
The new strategy comes after last week’s disastrous by-election losses led to warnings the prime minister is "doomed to lose power" if he does not change course.
But the row over the prime minister’s language risks echoing the outcry over Labour’s attack ads which claimed the PM does not think child sex abusers should go to prison, and which also led to accusations of “gutter politics”.
In a tweet, Mr Sunak said: "The Labour Party, a subset of lawyers, criminal gangs - they're all on the same side, propping up a system of exploitation that profits from getting people to the UK illegally. I have a plan to stop it."
He was supported by the energy security secretary Grant Shapps, who tweeted: "Labour seem to want criminal gangs and deceptive lawyers to decide who comes to the UK - that's why they tried to block every vote on stopping the boats."
Hitting back Mr McMahon said: "When all else is lost, the only place you have is the gutter.”
He added: "Poor yes. Desperate and pathetic from Sunak too."
Labour MP Chris Bryant, who chairs the Commons standards committee, also condemned the Prime Minister's language. "In his desperation he has plumbed a new depth," he said.
Mr Sunak’s tweet followed a story in the Daily Mail which alleged that a number of solicitors had offered to help an undercover reporter posing as an economic migrant submit a fake application, in return for thousands of pounds.
