Prime Minister Boris Johnson blamed his opposition Labour rival for Britain's failure to leave the European Union by Thursday's deadline and promised to deliver Brexit by January - if he wins the upcoming pre-Christmas election.

Johnson is riding high in opinion polls going into the December 12 vote that will be Britain's third in four years. 

But he risks a backlash over his unkept "do or die" promise to take Britain out by October 31 - and again set himself up for another potential fall by promising to meet the next deadline.

The Conservative leader, who wants no more delays to the process, cast himself as a victim of parliamentary opposition parties that refused to follow the wishes of UK voters who chose to leave Europe in the knife-edge 2016 referendum.

"After three-and-a-half years, it was perfectly obvious to me that this parliament is just not going to vote Brexit through," Johnson said during a campaign stop at a hospital.

"If you vote for us and we get our programme through, which we will - as a I say, it's oven-ready, it's there to go - we can be out, at the absolute latest, by January next year."

'It's not about me'

Pro-EU campaigners and business executives breathed a sigh of relief that Britain had been given a stay of execution to avoid a Halloween Brexit nightmare that could have seen it crash out of the bloc after 46 years without a plan.

Johnson confounded expectations by securing a revised EU divorce deal that Brussels had long refused to touch.

But he was forced to follow through on parliamentary orders and ask EU leaders for more time after Labour mustered enough cross-party support to extend parliamentary debates and delay a final vote.

Labour leader Jeremy Corbyn said he would throw out Johnson's plan and get Brexit "sorted" within the first six months of grabbing power by negotiating more EU-friendly separation terms.

He would then put it up for a vote against the option of simply staying the 27-nation bloc.

"We'll let the people decide whether to leave with a sensible deal or remain. It really isn't that complicated," Corbyn told a party rally at a London art centre.

"And we, the Labour government, will carry out whatever the people decide."

But the veteran socialist avoided answering a direct question on which way he himself would vote.

"It's not about me, it's not any individual on this platform, it's not a presidential election," Corbyn said.

'Government that cares'

Corbyn has been accused of seeking to shift the debate onto more domestic subjects such as health and social care to avoid scrutiny of his own vague position on Europe.

He has said in the past that he voted to leave in 2016. But he has also spent much of his political career attacking Brussels as a cauldron of crony capitalism.

Corbyn promised to push the most "radical" agenda Britain has ever seen. He pledged to put "wealth and power in the hands of the many" and eliminate everything from poverty to university tuition fees.

"Together we can pull down the corrupt system to build a genuine government that cares for all," he said.

Business leaders warn that Labour's plan to reimpose state ownership over railways and other major industries would cost at least £196 billion (€228 billion).

But a National Institute of Economic and Social Research study suggested Wednesday that Johnson's Brexit deal could leave Britain £70 billion worse off in 10 years. 

Outgoing MPs blame abuse

Almost 60 members of the 650-seat lower House of Commons have announced they will not stand in the coming election.

The number has raised eyebrows because - while dozens usually leave before general election - many came from the more moderate and wing of Johnson's party.

Senior cabinet minister Nicky Morgan was one of several to at least partly link her decision to the "abuse" lawmakers receive from the public.

Divisions over Brexit have seen sometimes toxic rhetoric on all sides. Death threats against lawmakers and attacks on social media have risen in recent years.

Morgan described the "clear impact on my family and the other sacrifices involved in, and the abuse for, doing the job of a modern MP".

Long-standing Conservative MP Caroline Spelman warned of a "wild west of internet abuse" as she stepped down.