A former justice of the UK Supreme Court today savaged Boris Johnson's new plot to "sabotage" a delay to Brexit .

Lord Sumption said it would be illegal for the Prime Minister to use a crafty method to avoid getting an extension from the EU.

The EU Withdrawal (No6) Act - set to become law today - will force the embattled PM to write to Brussels asking for a three-month delay if MPs haven't agreed a course of action by October 19.

But reports say the PM is now considering writing a second, parallel letter saying he doesn't want an extension and it serves no purpose.

That way the 27 EU leaders would be more likely to reject Britain's request and force a no-deal Brexit on October 31.

A No10 source told the Telegraph: "We intend to sabotage any extension... There's a good chance we won't be offered a delay."

Yet 70-year-old Lord Sumption, who was one of the 12 Supreme Court justices from 2012 to 2018, today declared that would be illegal.

(Image: REUTERS)

The QC dubbed the 'brain of Britain' told the BBC: "The Bill, or Act as it's about to become, says that he's got to apply for an extension. Not only has he got to send the letter, he's got to apply for an extension.

"To send the letter and then try to neutralise it seems to me, plainly, a breach of the Act.

"What you've got to realise is the courts are not very fond of loopholes."

Lord Sumption - who in May branded Mr Johnson a "clown" and Tory Brexiteers "grim fanatics" - went even further when asked what would happen if the PM refused to send a letter at all.

The retired judge said: "He would be in contempt of court.

"He would I suspect have to put up with the resignation of the Justice Secretary and Attorney General and probably other members of his Cabinet."

Amid claims the Prime Minister could even be jailed, Lord Sumption said: "There are plenty of ways in which this kind of obligation can be enforced."

The slapdown came as Mr Johnson faces defeat for the second time tonight when he asks MPs to back a snap general election on October 15.

Opposition MPs warned they would vote down the Prime Minister's bid, because they don't trust him not to force through no-deal Brexit.

If he loses, Boris Johnson is set to formally shut down Parliament tonight - meaning it won't sit again until a Queen's Speech on October 14 - despite thousands taking to the streets against the decision on Saturday.

(Image: AFP/Getty Images)

MPs could table a last-ditch emergency debate this afternoon to discover if Mr Johnson misled Parliament over the prorogation - which he claimed was nothing to do with Brexit.

And MPs will from 4.30pm debate a petition backed by 1.7million people against proroguing Parliament.

But despite the protests it's understood there is little MPs can to do stop prorogation - guaranteed by Thursday - taking place.

Meanwhile the Prime Minister is heading for a Supreme Court battle as he digs in his heels over his plan to get round the law against no-deal.

A former Director of Public Prosecutions said the Prime Minister could go to jail if he refuses to delay Brexit in the face of legal action. Lord MacDonald said a court may order “the law should be followed”.

(Image: AFP/Getty Images)

As shock predictions swirl around Westminster, some MPs fear the Prime Minister could even try to declare a national emergency to force no-deal.

And WhatsApp messages leaked to BuzzFeed last night showed some Tory MPs - including Sheryll Murray and Chris Green - apparently urging the PM to break the law to "deliver the referendum decision" on Brexit.

But Justice Secretary Robert Buckland was forced to step in on the group, telling MPs: "This government, like its predecessors, observes the rule of law at all times and for all seasons."

And as the PM visits Ireland's premier today in Dublin, The Times reports Mr Johnson has privately accepted he will have to delay Brexit - but only if it's forced on him by the courts.

(Image: AFP/Getty Images)

Mr Johnson is still pushing ahead with plans for a Queen's Speech despite having a majority of minus 45 - casting doubt over whether it will pass through the Commons.

DWP Secretary Amber Rudd resigned from the Cabinet and Tory whip on Saturday, joining 21 rebels who were stripped of the whip last week.

She launched an excoriating attack on the Prime Minister accusing him of an "assault on decency" and an "act of vandalism".

Show more

And she only told him about her decision on the phone at the same time as a resignation interview appeared online.

But pro-EU Cabinet ministers Nicky Morgan and Julian Smith today both signalled they would not be following Ms Rudd out the door.