UK MPs, including Tories expelled from the party, are preparing legal action in case Prime Minister Boris Johnson refuses to seek a delay to Brexit.

According to the BBC, a bill requiring Johnson to ask for an extension to the UK’s departure date to avoid a no-deal Brexit on October 31 is set to gain royal assent.

But the Prime Minister reportedly wrote to Tory members on Friday evening pledging to break the law that will require him to seek an extension of article 50. “They just passed a law that would force me to beg Brussels for an extension to the Brexit deadline. This is something I will never do.”

He said he would not entertain seeking another deadline extension from Brussels, as the incoming law, expected to receive royal assent on Monday, compels him to if no agreement is in place by October 19. “I will not. I don’t want a delay,” Johnson said.

Now MPs have lined up a legal team and are willing to go to court to enforce the legislation, if necessary, said the BBC.

The cross-party bill – which requires Johnson to extend the exit deadline until January unless Parliament agrees on a deal with the EU by October 19 – was passed on Friday.

Although the government has said it will abide by the law, Johnson described it as obliging him “in theory” to write to Brussels asking for a “pointless delay”.

Downing Street said the British public had been clear that they wanted Brexit done.

David Lidington, Theresa May’s former de facto deputy Prime Minister, said it would set a “dangerous precedent” if Johnson chose to disobey the law.

Lidington said that at a time when other countries were “holding up alternatives to the rule of law and democratic government” it was imperative that British governments always demonstrate they comply with the law.

He resigned as Cabinet office Minister in July, in opposition to Johnson’s no-deal Brexit strategy.

This week, however, he supported the government in voting for an early general election. He said he had been “persuaded” by Johnson that he “was serious about getting a deal”.

The bill, presented by Labour MP Hilary Benn, says Johnson will have until October 19 to either pass a deal in Parliament or get MPs to approve a no-deal Brexit.

Once this deadline has passed, he will have to request an extension to the UK’s departure date to January 31, 2020.

Unusually, the bill stipulates the wording of the letter Johnson would have to write to the European Council President.

If the EU responds by proposing a different date, the Prime Minister will have two days to accept that proposal. During that time, MPs – not the government – will have the opportunity to reject that date.