Update (10 June): Chris Curtis has deleted the initial tweets reported below and clarified that the results of the election poll he discusses were pulled "because of concerns other members of the team had about the methodology". He said he was “happy to clarify the position and apologise to YouGov for any confusion caused" and had not intended to suggest Nadhim Zahawi played a role in suppressing any poll results. Curtis said he still believes the survey was "conducted to the highest standard".
A polling company has denied banning the release of a poll during the 2017 general election campaign because the results were "too positive" towards Jeremy Corbyn.
Chris Curtis, a former employee at YouGov who worked at the company during the 2017 general election, claimed that after a leaders debate polls showed Corbyn had won "by a mile" and one in four Tory voters thought the Labour leader was the better candidate.
Theresa May ended up being the victorious candidate, remaining as prime minister but seeing a net loss of 13 constituency seats, but the result of the election was far closer than many had initially predicted.
In a long-ranging Twitter thread, Curtis said in the lead-up to the election, polls had been increasingly favourable towards Labour, and that "each day the gap just kept getting smaller and smaller."
He added: "On the morning of the Manchester bombing, we actually had Labour pulling level, although the poll got spiked because the campaign rightly paused."
When they released the methodology behind the polling showing Labour in an increasingly positive light, Curtis said it showed "exactly the same thing as our standard polls would have, but it was the first time anybody had said 'hung parliament'."
Curtis added there was a "backlash" to the release of the methodology, leading to a "panic" at YouGov.
He went on to claim Tory MP Nadhim Zahawi threatened to call for the resignation of Stephen Shakespeare, YouGov's CEO, if they released the date and it was wrong.
"Nadhim Zahawi called up the CEO and said he would call for his resignation if he was wrong. It became pretty clear we would all be out of a job if we were wrong now," Curtis claimed.
Shortly after the call, a televised debate between the party leaders was held, which produced data which Curtis claimed showed a "clear" winner.
Curtis said: "We did a fantastic debate poll in the hours following the debate that Corbyn took part in. The results were stark - Corbyn won by a country mile, and one in four Tory voters thought he was best.
"Despite having written the story and designed the charts, we were banned from releasing the story because it was too positive about Labour."
Zahawi has denied the claim he was serious about calling for Shakespeare's resignation, saying it was a joke between the pair.
He wrote on Twitter: "This was clearly a joke between two good friends, who had previously been business partners for several years.
"Stephan continues to be one of my closest friends and at no point since leaving YouGov in 2010 have I had any influence on the company. Suggesting otherwise is untrue."
YouGov vehemently denied the allegations, and in a statement said: "Chris Curtis’s allegation that we suppressed a poll because the results were 'too positive about Labour' is incorrect. There was a poll run by Chris following the debate in Cambridge on May 31, 2017.
"When reviewed by others in the YouGov political team, it was clear that the sample of people who watched the debate significantly over-represented Labour voters from the previous election.
"We take our responsibilities as a research organisation seriously and we could not have published a poll from a skewed sample that favoured any party. No serious polling organisation would have published this.
"The idea that YouGov would suppress a poll that was 'too positive about Labour' is plainly wrong – as evidenced by the fact that in the 2017 election YouGov published an MRP model showing Labour doing significantly better compared to most other polling organisations."
Curtis posted a follow-up thread later on Wednesday saying he hadn't realised his comments would be such a "big deal".
He stated he was not accusing Zahawi of YouGov changing its results to "suit Tory ends", but re-iterated his initial claims that the Corbyn poll was valid to publish. But, he acknowledged: "It may have been true that Labour voters were more likely to have watched the debate than Conservative voters and therefore taken part in the questions about the debate."