Boris Johnson’s chief whip has reached out to Tory Brexit rebels with letters outlining how they can appeal against the prime minister’s decision to sack them from the party.

Johnson caused uproar within the Tories by removing the party whip and barring from standing as an election candidate 21 backbenchers who helped the Commons pass a law aimed at blocking a no-deal Brexit.

Amber Rudd criticised the decision when she quit the cabinet and the Tory whip to join the rebels at the weekend.

Chancellor Sajid Javid has been among those senior ministers calling for the sacked MPs to be readmitted.

A rebel source said chief whip Mark Spender told rebels that he “took no joy in removing the whip” and outlined how they could appeal the decision.

Spencer, who has rebelled 11 times since the Tories took power in 2010, also stressed: “For too long the Conservative party has been hampered by those that believe the normal rules of party politics do not apply to them.”

The source described the letter as “firm and unapologetic” and said it was unclear whether the chief whip was setting out the party’s position legally or opening up lines of communication in case Johnson needs the MPs to back any new Brexit deal he puts before the Commons next month.

“It is not really clear until we all know what Dominic Cummings next ‘cunning move’ is,” the rebel source said.

Ex-chancellor Philip Hammond, who has vowed to fight in the courts if necessary to be readmitted to the Tories, was among those in correspondence with Spencer.

Many of the rebels, if not all, are understood to have received the letter.