Rebecca Long-Bailey has said it is “bollocks” to claim voters don’t want socialism, despite Labour’s heavy election defeat.

The shadow business secretary, who is a favourite to be the party’s next leader, also accused Labour MPs of deleting shadow cabinet files in an effort to undermine Jeremy Corbyn.

In a recording leaked to HuffPost UK, Long-Bailey promoted herself as unfailingly loyal to the outgoing leader, who remains highly popular with members, and claimed shadow ministers who resigned en masse in 2016 of tr to sabotage her work.  

She was speaking at the retirement dinner of ex-Blyth MP Ronnie Campbell on Saturday evening.

The shadow business secretary said Boris Johnson’s election victory in December left her “in a state of shock” because “everybody loved the Labour Party” in the “people’s republic of Salford”, where she is an MP.

“We had a few wobbly people on the doorstep because of Brexit, but I thought everything was going to be alright,” she said. 

She said she believed in the “worst case scenario it would be a hung parliament” but the exit poll left her “crushed”.

Long-Bailey said: “I was in a state of shock and it was as if everything I believed [was] being ripped up before my very eyes, that everything we fought and we’re so proud of was suddenly invalidated, [that] no-one wanted us, no-one wanted socialism.

“And then I pushed that thought out of my head because I thought ‘that’s bollocks’.”

Long-Bailey was praised by Corbyn as “totally dedicated” at the same event.

Long-Bailey was part of John McDonnell’s shadow Treasury team in 2016.

In her speech on Saturday she said files went missing after Labour MP Rob Marris resigned as a shadow minister and “flounced off” during a committee meeting in parliament. 

When proceedings were abandoned, Long-Bailey said she ran back to her office “because I had a feeling that something wasn’t right here” and was told the files had gone. 

She described the document as being held on a “shared drive” and the product of “months and months and months” of meticulous work mapping out the team’s bid to oppose the government’s finance bill. 

Long-Bailey said after the resignations she and McDonnell were left in the Treasury team, as Corbyn’s criticis hoped they would be “smoked out”.

She said: “I went in and I spoke to John and I started ranting and I think my exact words were ‘if they think they are going to get rid of us then they’re going to have to carry me out kicking and screaming’ and I sat in that office until about 3am going through all the clauses. 

“Richard Burgon was dragged in at one point. Angela Rayner was dragged in and she got us a Domino’s pizza because we were starving and we got through the clauses and we went to the finance bill committee the next day fully prepared and I was pretty good if I’m honest.” 

The story will be seen as a thinly veiled attack on her rivals Lisa Nandy, who resigned as shadow energy secretary, and Keir Starmer, who resigned as shadow home office minister. 

Marris was among a huge cohort of Corbyn-sceptics who resigned and forced the 2016 leadership challenge which saw Owen Smith defeated. Marris stood down before the 2017 general election. 

He strongly denies there was any malicious intent but said that his assistant deleted the files because the document was created by his parliamentary office and was not the property of the Labour Party. 

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“She is trying to imply I stole Labour Party information,” he said, adding: “My assistant removed from the computer documents which my office created using my parliamentary expenses. That information was not paid for by the shadow Treasury team, it was paid for by parliament and it belonged to me.” 

Speaking on the same platform as Long-Bailey on Saturday, Corbyn also claimed “the information that she should have had in order to fight the Tories’ finance bill mysteriously went missing”.

Heaping praise on his favoured successor, who was last week endorsed by the powerful Unite union led by Len McCluskey, he went on to say she “gave an absolutely brilliant performance, because she was totally dedicated to standing up for our party against the Tories”. 

In a clear if not explicit endorsement of Long-Bailey, he told the crowd: “It’s an absolute pleasure to be here alongside Becky Long Bailey, our candidate for leader. 

“I’ve known Becky since we came in to parliament and we’ve worked very well together. She has done the most to develop our trade union policies.”

Long-Bailey, who faces competition for the top job from Nandy, shadow Brexit secretary Keir Starmer and shadow foreign secretary Emily Thornberry, has repeatedly faced criticism she is the “continuity Corbyn” candidate. 

The winner of the leadership race will be announced on April 4.