Suella Braverman plans major intervention to undermine Rishi Sunak as PM braces for SOARING migration numbers

The Conservative Party under David Cameron was elected in 2010 on a manifesto pledge to bring net migration down to below 100,000.

WATCH: Ben Habib describes Suella Braverman as the 'last true conservative'

An ally of Braverman told Politico she will stage an intervention if she believes the figures to be "unacceptably high".

This would be yet another knock for the Government, which was dealt a blow when the Supreme Court deemed its plan to send migrants to Rwanda unlawful.

All five justices unanimously agreed with the Court of Appeal’s conclusion that the Rwanda policy was unlawful.

Giving a press conference later that day, the Prime Minister said he will introduce emergency legislation declaring Rwanda a safe country.

Earlier that day, following hte judgement, Braverman had urged Sunak to introduce such legislation, demanding he “block off ECHR, HRA, and other routes of legal challenge”.

The former Home Secretary, who was sacked earlier this month after publishing an unauthorised Op-Ed criticising the police, sent a scathing letter to Sunak after she left office criticising his record on tackling migration.

She accused Sunak of "betraying" the mission to "stop the boats", claiming he "rejected" available options she presented to him, such as "blocking off" the European Convention on Human Rights and the Human Rights Act.

She said: "I was clear from day one that if you did not wish to leave the ECHR, the way to securely and swiftly deliver our Rwanda partnership would be to block off the ECHR, the HRA and any other obligations which inhibit our ability to remove those with no right to be in the UK.

"Our deal expressly referenced ‘notwithstanding clauses’ to that effect.

"Your rejection of this path was not merely a betrayal of our agreement, but a betrayal of your promise to the nation that you would do 'whatever it takes' to stop the boats."

Braverman also accused Sunak of failing to "prepare any sort of credible 'Plan B'."

She wrote: "At every stage of litigation I cautioned you and your team against assuming we would win. I repeatedly urged you to take legislative measures that would better secure us against the possibility of defeat. You ignored these arguments. You opted instead for wishful thinking as a comfort blanket to avoid having to make hard choices. This irresponsibility has wasted time and left the country in an impossible position.

"If we lose in the Supreme Court, an outcome that I have consistently argued we must be prepared for, you will have wasted a year and an Act of Parliament, only to arrive back at square one. Worse than this, your magical thinking — believing that you can will your way through this without upsetting polite opinion — has meant you have failed to prepare any sort of credible ‘Plan B’.

"I wrote to you on multiple occasions setting out what a credible Plan B would entail, and making clear that unless you pursue these proposals, in the event of defeat, there is no hope of flights this side of an election. I received no reply from you."