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"We are now the mainstream", Jeremy Corbyn has declared as he gears up for a conference billed as Labour's biggest ever.

Thousands of activists will descend on Brighton tomorrow for the first time since snatching away Theresa May's majority.

The Labour leader will kick off the bash with a mass rally after he secured his position following months of resignations and attempts to oust him.

And he'll be in victorious mood after rule changes made it easier to have a left-wing successor when he leaves.

Mr Corbyn has branded the conference "the biggest we've ever held" while party chair Ian Lavery, a key ally, today announced Labour membership had risen to 569,500.

In another boost today Labour was given a four-point lead over the Tories in a new poll.

(Image: Daily Mirror)

The Ipsos MORI political monitor showed belief in Theresa May as a capable leader has fallen 23 points since September 2016 to 45%.

That was still ahead of Mr Corbyn on 38%.

But overall voting intention was 44% for Labour and 40% for the Conservatives.

Two in five (40%) say Mr Corbyn has sound judgment (up 10 points), 52% say he understands the problems facing Britain (up eight points) and 47% say he has a clear vision for Britain (up nine points).

The phone survey of 1,023 British adults between September 15-18 put the Lib Dems on 9%.

Labour's leader told The Guardian: "The election has changed politics in this country. We are now the mainstream."

(Image: Getty)

Branding the government one in "disarray", he added: "We will use our strength in parliament and our support in the country to challenge the Tories at every step.

"Wherever we can, we will block their attempts to pay for tax cuts for the richest by making life worse for millions of people."

Despite Labour tensions rising over Brexit , and himself suffering scores of resignations since 2015, Mr Corbyn insisted Boris Johnson's disloyalty would not happen on his watch.

The Foreign Secretary publicly tripped up Theresa May by publishing his own vision of life after Brexit just a week before she publishes hers.

Mr Corbyn claimed the lapse of discipline “would not happen” in his own shadow cabinet team.

Labour's preparations for a possible election include targeting top Tories in now-marginal seats including Amber Rudd , Boris Johnson and Iain Duncan Smith.

Mr Corbyn also plans to restart his tour of marginal constituencies as he reissues his claim Labour is ready for an election.

The party is currently selecting candidates in key seats and putting policy papers together.

Gideon Skinner, head of political research at Ipsos MORI, said: "The public have clearly warmed to Jeremy Corbyn 's style and cooled on Theresa May, over the last year.

"Since 2007, the Conservatives used to be able to offset being the less-liked party with a more-liked leader, but now they are behind on both.

"But Theresa May still leads on some competence issues such as capability and handling a crisis - although even these have taken a big hit from her commanding position a year ago."

A Tory spokesman dismissed Mr Corbyn's comments, saying "Labour's top team are hopelessly divided" on issues including Brexit, economic policy and Trident and "the simple fact is they're not fit to govern - and it's people who would pay the price for that failure".