LONDON   -   MPs, including Tories expelled from the party, are preparing legal action in case the PM refuses to seek a delay to Brexit.

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

But the PM has said he would “rather be dead in a ditch” than ask for a delay.

Legal experts have warned the prime minister could go to prison if he refuses to comply with the new law.

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

The cross-party bill - which requires the prime minister to extend the exit deadline until January unless Parliament agrees a deal with the EU by 19 October - was passed on Friday. Although the government has said it will abide by the law, Mr 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. Labour leader Jeremy Corbyn told BBC News the party was not taking legal action over the legislation, but said it was “aware of the actions that are being discussed and prepared for”.

He added that Labour would allow a general election “when we are clear that there will be an end to the danger of no-deal on 31 October”. “We need a clear statement from the prime minister that he is going to abide by that act of Parliament,” Mr Corbyn said.

Several hundred people joined pro and anti-Brexit protests in Parliament Square in London on Saturday. Some 35 other events are being held across the UK and Europe, including a pro-democracy protest in Berlin.

The Daily Telegraph reported that the prime minister said seeking another extension is “something I will never do”, fuelling speculation that ministers could try to find a loophole. But David Lidington, who resigned as Cabinet Office minister in July, in opposition to Mr Johnson’s no-deal Brexit strategy, told the BBC’s Today programme: “The government is bound by the words of any statute that has been duly enacted by the Queen in Parliament, which is a fundamental principle of our constitution and our ministerial code.

“Defying any law sets a really dangerous precedent.”

He added 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.

Mr Lidington, who supported the government in voting for an early general election, urged Mr Johnson to “re-double [his] efforts” in talking to a “wide range” of European leaders to get a Brexit deal he can put before Parliament in October.

What are the PM’s options?

Mr Johnson’s options are “narrowing” after this week’s Brexit defeats, says Dr Hannah White, deputy director of the Institute for Government.

Some possibilities being discussed are:

Ignore the law - Boris Johnson has said he “will not” carry out Parliament’s instructions to seek an Article 50 extension, according to The Daily Telegraph. But unless he finds a legal loophole, this could land the prime minister in court and further divide his party.

Resign - He could quit as PM with the tactical aim of getting back in, letting Jeremy Corbyn go to Brussels for an extension before triggering a general election he would hope to win. Dr White calls this “risky”, with no guarantee the Queen would nominate Mr Corbyn as interim leader. The tactic could otherwise backfire, going down badly with voters and handing other advantages to the opposition

A one-line bill - The PM could try again to secure an early election by proposing a “one-line bill” simply stating there will be one despite the Fixed Terms Parliaments’ Act. It would need just a simple majority to pass but it is also “risky” because MPs could table amendments to it, including changing the election date

Scrap the law - If he could get an election before 19 October and win it with a majority, he could, in theory, repeal the new law and therefore not be required to request an extension.

EU veto - If the PM is forced to ask Brussels for an extension, there is no guarantee they will accept it. All 27 EU member states need to agree to it, so Mr Johnson could persuade one of the countries to veto it.

Former attorney general Dominic Grieve has warned the prime minister “could be sent to prison” if he refuses to obey the law and delay Brexit.

Grieve told BBC News Mr Johnson would be “under an obligation” to abide by the law after it has received royal assent.