Bosses at YouGov suppressed publication of a poll during the 2017 election campaign because it was "too positive about Labour", a former manager at the pollster has claimed.
Chris Curtis said a poll conducted after a key leadership debate showed Jeremy Corbyn had won "by a country mile" but that the pollster banned its release while under pressure from its Tory MP founder.
YouGov denies Mr Curtis's characterisation of events and says the poll was in fact pulled because it had "a skewed sample" – but Labour figures branded the claims "shocking" and said they raised questions about "the health of our democracy".
In a post on social media on Wednesday Mr Curtis, who is now head of political polling at competitor Opinium 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.
"But despite having written the story and designed the charts, we were banned from releasing the story because it was too positive about Labour."
Mr Curtis said YouGov bosses had "panicked at the backlash" to earlier research correctly predicting a hung parliament – against all expectations.
He said Nadhim Zahawi, a Conservative MP who co-founded the company in the year 2000, telephoned YouGov's chief executive and "said he would call for his resignation if he was wrong".
Mr Curtis added: "It became pretty clear we would all be out of the job if we were wrong now." He clarified that Mr Zahawi had not “directly had a hand” in the decision on the individual poll, however.
The firm's polling methodology was also tweaked for the final poll before the election to increase the Tory lead "after pressure from high-ups and despite protests from those of us who thought it wasn't ok", he added.
John McDonnell, who was shadow chancellor at the time, told The Independent: “This is a shocking but immensely important revelation. It throws into question the integrity and independence of polling on this country.”
The Labour MP said he believed the “bulk” of the media were “working overtime to prevent Labour being elected”, and added: “To find out that polling was being manipulated against us takes the debate about the health of our democracy to a new level.”
James Schneider, who was head of strategic communications for Labour at the election, said the claim "more than confirms my suspicions at the time about modelling meddling".
Labour came from well behind the 2017 election to overturn Theresa May's majority and increase its vote share to 40 per cent.
YouGov's MRP model was the first survey to correctly predict this result, including down to some individual seats.
The company was founded by Mr Zahawi, who was later elected a Tory MP in 2010, and Stephan Shakespeare, a former Tory candidate from the 1997 election. Mr Zahawi currently does not hold a formal role with the company.
A spokesperson for YouGov told The Independent: "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 31st May 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."
Responding to YouGov in follow-up comments, Mr Curtis said he believed the poll in question was conducted in “exactly the same way as we ran this other debate poll, which nobody had any problem with us publishing”.
And he added: “The most important finding of the poll, the one I wanted to focus on and thought was most important, was that a good chunk of Tory voters thought Corbyn had won. This is rare in a debate poll where results normally fall down party lines.”
Mr Zahawi, who is now education secretary, confirmed that he had spoken to YouGov’s chief executive, but said his comments about dismissing the boss were made in jest.
"This was clearly a joke between two good friends, who had previously been business partners for several years," he said in a statement posted on social media.
"Stephan [Shakespeare] 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."
On 9 June 2022 the sub-headline of this article was amended to remove any suggestion that Mr Zahawi’s phone call was linked to the decision to pull the poll.
