Rishi Sunak is facing a growing Tory rebellion over his flagship Rwanda bill.
Senior MPs on the right of the party say they will vote against the legislation unless it is made tougher.
They include former cabinet minister Simon Clarke, who today said it was currently “riddled with holes”.
Sunak has insisted the Safety of Rwanda Bill is needed to finally allow the government to deport asylum seekers to the east African country.
But dozens of Tory MPs - including deputy party chairman Lee Anderson - are backing amendments to the bill which would allow ministers to ignore rulings by the European Court of Human Rights.
The prime minister has been warned, however, that moderate Conservative MPs will vote against it if he caves in to the right-wing rebels.
The bill returns to the Commons on Tuesday and Wednesday for MPs to debate and vote on it.
Clarke, who served under Boris Johnson and Liz Truss, said: “I have been clear with the whips that if the bill goes forward unamended, I will be unable to offer it my support.
“I am prepared to vote against it myself because we have twice now marched the British public up the hill of legislation to enable the Rwanda plan to take effect. We have failed twice.
“It is best that we don’t maintain what is a polite fiction that a bill which is still riddled with holes for people with creative lawyers to exploit will do the job.”
Former home secretary Suella Braverman has also said she will vote against the bill if it isn’t made tougher.
If enough rebels join forces with opposition parties in opposing it, the PM could face the humiliation of his flagship legislation being rejected by the Commons.
Sunak today insisted he was willing to talk to the rebels, but stopped short of saying he would accept any of their amendments.
He told GB News: “I’ve always said that I’m happy to have a dialogue with anyone who thinks they might have an idea that will improve the effectiveness of the bill whilst making sure that it’s still legally compliant and maintains Rwanda’s participation in the scheme.
“We might have all the ideas you want, but ultimately, that means Rwanda will stop participating in the scheme. That’s no good at all. Because a policy without anywhere to send people to isn’t a policy that’s going to do anyone any good.
“I am happy to have that dialogue. I’m confident that the bill that we’ve put forward will work.”