Jeremy Corbyn has promised a raft of new “organising academies” to train Labour activists for the next election, as his leadership rival Owen Smith accused him of being “delusional” about the party’s chances of beating the Conservatives in 2020.

The Labour leader set out plans on Tuesday for a new training camp for Labour members in every region of the UK in order to help turn many of the hundreds of thousands of new joiners into active community organisers.

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Corbyn said the plan would put the party’s 500,000 members at the front of Labour’s strategy to win the next general election, claiming it “represents the single biggest commitment by any political party in British history to aid in the learning and training of its members”.

In recent leadership hustings, the Labour leader claimed that the party had been ahead in the polls against the Conservatives before MPs started rebelling against his leadership after the EU referendum.

This was challenged on Tuesday by Smith, who said this was not an honest representation of polls. He suggested Labour had been behind in the vast majority since Corbyn became leader.

“I think that’s delusional, and I think Jeremy needs to think a bit more about that straight, honest politics that he started his campaign with,” Smith told the BBC.

“The straight, honest truth is that we are right now at our lowest ebb in the polls, ever. If there was an election tomorrow Labour would be decimated, and that’s got to be a shock to Labour’s system.”

Smith claimed Labour could lose almost 40% of its MPs if it continued on what he called the party’s “disastrous trajectory”.

“If Jeremy is deluding himself that we are heading to victory, I do not think the rest of the party or the country can afford to be deluded about where we are,” he said, claiming Labour was “in the doldrums” and that it faced “Groundhog Day” if Corbyn won.

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Corbyn is the strong favourite to retain the leadership when the result is announced at the party’s conference in just under two weeks’ time.

On Tuesday he said pledged to make the Labour membership an “even more active force for good in every single community, ensuring that Labour mounts the most successful electoral campaign imaginable”.

“The size of our membership means that the Labour party will be a visible presence in every neighbourhood, urban or rural, in every part of our country, not just at election times but all the time,” he said, claiming Labour was now Europe’s biggest political party by membership.

The Labour academies will be situated in every region of the UK, with accredited courses on media and communications, digital, politics and policies. The training will support members to listen to, engage with and persuade people.

Some of the work will be concentrated on post-industrial communities where Labour faces a significant threat from Ukip, with a targeted campaign fund and additional organising focus on these areas.