Rishi Sunak is facing a rebellion by right-wing Tory MPs over his flagship Rwanda bill.
Around 30 backbenchers are backing amendments aimed at toughening up the legislation, which is aimed at finally getting deportation flights to the African country off the ground.
They want the government to be able to ignore rulings by the European Court of Human Rights blocking flights from taking off, as well as making it harder for immigrants to appeal.
But that is fiercely opposed by moderate Tory MPs, who have threatened to vote against any attempts to make the bill tougher when it returns to the Commons next week.
The right-wing rebellion is being led by former immigration minister Robert Jenrick, who resigned in protest last month.
He said as it is currently drafted, the Safety of Rwanda Bill will not stop the small boats carrying asylum seekers across the English Channel.
Jenrick said: “The stakes for the country could not be higher.
“If we don’t fix this bill the country will be consigned to more illegal crossings, more farcical migrant hotels and billions more of wasted taxpayers’ money in the years to come.
“If the government truly want to stop the boats, it should adopt these amendments and use parliament’s power to deliver on the repeated promises we have made the public.”
Among the high-profile Tory MPs backing Jenrick are Jacob Rees-Mogg, Suella Braverman and Iain Duncan Smith.
However, members of the One Nation Caucus of moderate are urging Rishi Sunak to reject the right-wing amendments.
Speaking at an event last night, one of its members, Matt Warman MP, said: “We can’t re-write our international obligations for our sole self-interest.
“We’ve got faith that Britain is who we are because it can take a leading role in the world. We can rebuild institutions like the ECHR from within - institutions that we helped to build in the first place.”