Lee Anderson and Brendan Clarke-Smith quit as deputy chairmen after siding with rebels, while ex-immigration minister Robert Jenrick and others said they were ready to defy the government at the showdown vote later on Wednesday.
If around 30 of the rebels carry out their threat, Mr Sunak will be handed a humiliating defeated – potentially sparking yet another Tory leadership contest or a general election within weeks.
Mr Sunak’s allies claim the risk of an early election – with an almost certain big Labour victory – will make the rebels will back off, allowing the PM and his battered administration to live to fight another day.
In a sign that No 10 is looking at fresh concessions to the Tory right-wing rebels, Mr Sunak’s illegal migration minister Michael Tomlinson said ministers were considering tweaking the civil service code to remind officials to follow ministerial decisions.
It comes amid concerns by Tory rebels that the Rwanda legislation fails to go far enough to block last-minute, rule 39 injunctions from the European Court of Human Rights (ECHR).
Mr Tomlinson told BBC Radio 4’s Today programme: “My expectation is that there will be further confirmation that it will be for ministers to decide and then, once those decisions are made, they will be carried out ... by our excellent and efficient civil servants.”
Sir Jacob Rees-Mogg has warned Mr Sunak that his vote on the Rwanda bill depends on a guarantee that ECHR rulings can be ignored. “Will the attorney general basically agree that a Rule 39 order can be overruled? If that’s the government’s position, that’s really important.”
But one senior Tory rebel told The Independent they were “not particularly impressed” by the assurance the code would be tweaked.
No 10 said is “not right” to say that the government is seeking to rewrite the civil service code over its Rwanda plan. Mr Sunak’s official spokesman said there would be “additional guidance” for civil servants to give “clarity” on following ministers decisions in the application of the legislation.
Mr Jenrick has told MPs that the attorney general had advised ministers they could not ignore injunctions from the European Court of Human Rights (ECHR) as the law currently stands.
The leading Tory rebel – the former immigration minister – said it was “in theory at the discretion of a minister as to whether or not to comply” with a rule 39 injunction on Rwanda deportaions from the Strasbourg Court.
Mr Jenrick added: “Belying that, was the government legal advice that in its opinion, which I believe to be erroneous, it would be in breach of international law to do so.”
Deportation flights to Rwanda must take off regularly or the public will view the scheme as a “gimmick”, Tory MP Jonathan Gullis – who is considering rebelling – has said.
Mr Gullis told LBC the giovernment had to ensure “regular flights with lots of people on board, otherwise people will just see it as a gimmick, the voters will see it as a gimmick”.
He added: “We will have tried a third piece of legislation in three years and, if it fails, it will be three strikes and you’re out.”
Last night saw 60 Tory MPs back rebel amendments to the government’s Rwanda legislation, as well as the resignation of deputy party chairmen Mr Anderson and Mr Clarke Smith.
A close ally of Rishi Sunak has said most of the Tory rebels will “wimp out” when it comes to Wednesday evening’s crucial vote.
The senior Conservative MP told The Independent: “They will wimp out at the third reading. They’ll fall into line. Voting against the bill would force a general election now – so why would they do it?”
Another Tory MP loyal to Mr Sunak said: “Most realise to defeat the government to bring down one of its major policies on this would be political madness.”
Tory rebel Simon Clarke is the first to state explicitly that he will be voting against the Rwanda bill – a sign the most hardline of MPs have given up on getting assurances from No 10
In an op-ed for The Telegraph, the ex-Liz Truss minister claimed that a defeat for Rishi Sunak would not necessarily throw his premiership into crisis or force a general election.
“If the bill is voted down this evening, there will be one final opportunity for the government to return to parliament with a bill that works, and which can command the support of the whole of the Conservative party.”
Chancellor Jeremy Hunt insisted this morning that the party is united behind the principle of the Rwanda deportation scheme, saying devisions amounted to “lively debates”.
The chancellor said: “We are united in the Conservative party in our belief we need to solve this problem. Of course, we have lively debates inside the party about how to deliver the Rwanda policy.”
Labour leader Sir Keir Starmer claimed at PMQs that Mr Sunak had been “brutally exposed by his own MPs yet again” – arguing that Tories were in “open revolt against his [Rwanda] policy”.
Earlier this week a YouGov poll that suggested the Conservatives could see a 1997-style wipeout, gifting Labour a majority of 385 seats.