PM Theresa May plans a three-year "soft war" to kill Labour off. She will target more seats after the Tories’ Copeland by-election triumph.

She wants to launch a sustained offensive up to 70 of their most vulnerable seats to finish off Jeremy Corbyn’s wounded party.

5 Theresa May hailed the victory in Copeland yesterday Credit: Sky News

Some ministers have urged her to call a snap poll in the wake of her historic by-election victory in Labour-held Copeland.

But the PM has told aides she wants to exploit the party leader’s weakness by “slowly turning the screw” from now to 2020.

Tory strategists believe she can snatch up to 70 seats from Labour at the next general election – banishing them from power for decades.

5 Jeremy Corbyn says he is NOT to blame for disastrous of Copeland loss

A senior source said: “Theresa scented blood after Thursday’s stunning success – now she wants to go in for the kill.

“She’s resisting temptation to call an election now and is going for a slow death.

"The idea is to prolong Corbyn’s misery by keeping him in place and slowly digging out the ground from under his feet.”

Campaign teams will be sent to work relentlessly in a range of marginal seats which Tories now feel are within their grasp.

They include former northern strongholds of Halifax, Dewsbury, Wirral West and City of Chester.

Party workers will also flood Labour’s flimsy foothold in the south at Enfield North, Ilford North and Hampstead and Kilburn.

Some of them have not been held by the Tories since the early 1980s.

A party insider said: “It’s clear that traditional Labour voters are disillusioned with Labour’s lame duck leader.

“The plan is to devote time and energy in these areas to drive home the point that we are the real party of working people.”

5 Mr Corbyn insists he will lead the party into the 2020 election Credit: Getty Images

The “slow death” strategy is being drawn up after Tories took Copeland, a safe Labour seat since 1935, reversing Labour’s 2,564 majority at the last election.

It comes as a poll revealed nearly a third of voters would be more likely to back Labour if Mr Corbyn was replaced.

A whopping 34 per cent of Labour supporters admit they would be more likely to stick with the party if he went, according to the ComRes survey.

Six in ten Lib Dem voters and a quarter of Ukip supporters also say they would consider backing Labour with a different boss – but Mr Corbyn insists he will lead the party into the 2020 election.

Yesterday deputy leader Tom Watson urged him to take a "long hard look” at himself in the wake of Thursday’s historic defeat.

He said Labour should be looking to gain 100 seats at the next election rather than struggling to retain ones they hold.

But he stopped short of calling for Mr Corbyn’s to stand down, saying “this is not the time for a leadership election”.

The veiled criticism of the party’s direction came as Mr Watson addressed delegates at a Scottish Labour conference.

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Mr Watson said: “I want to be clear about this week’s by-elections. I’m not going to sugar coat the results. You deserve better than that.

“I’m glad we won in Stoke. Gareth Snell will be a great MP, and sending Paul Nuttall back home with his tail between his legs is exactly what he deserved.

“But I’m hugely disappointed that Gillian Troughton won’t be joining him in Parliament as the MP for Copeland.

“That means that all of us with leadership roles in the Labour party need to have a long, hard look at ourselves and what’s not working.

“Seven years into a Tory government, we shouldn’t be facing questions about whether we can retain the seats we already hold.

“Our job at the next election is to gain over 100 seats. Keeping what we have is supposed to be the easy bit.”

5 Deputy leader Tom Watson urged Mr Corbyn to take a 'long hard look' at himself Credit: PA:Press Association

Mr Watson – who attempted to negotiate Mr Corbyn’s departure during a summer coup last year – fell short of calling for the Labour leader to go.

“I’ve said it a lot recently. This is not the time for a leadership election. That issue was settled last year,” he said.

“But we have to do better. We cannot sustain this level of distance from the electorate, from our natural supporters.”

David Miliband said the shift to the Left under Corbyn was “a mistake” that won’t solve Britain’s problems.

The former Foreign Secretary – pipped in the 2010 Labour leadership battle by his brother Ed – said he would have joined 52 Labour MPs who rebelled against his backing for the Brexit Bill.

He added: “This isn’t just an electability question. It’s a question of substance.

“I think one can achieve more radical and substantive change through a different set of positions.”

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