YouGov has denied blocking the release of a poll that was “too positive” for Labour.

The explosive claim was made by former employee Chris Curtis who said that bosses at the firm stopped him from publishing the findings of a survey following a TV debate during the 2017 election campaign. 

He said it showed that Jeremy Corbyn had won "by a mile".

Taking to Twitter, Mr 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."

He said: “But despite having written the story and designed the charts, we were banned from releasing the story because it was too positive about Labour.”

Curtis also claimed that changes were made to YouGov’s polling methodology in the run-up to polling day which increased the Conservative lead.

He said: “This was done after pressure from high-ups (and despite protests from those of us who thought it wasn’t ok).”

In response, YouGov said in a statement: “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.”

Mr Curtis, who is now head of political polling at Opinium, insisted the TV debate poll was sound.

He tweeted: “On the methodology of the poll, it was done using the standard YouGov methodology that they use all the time. I am almost certain it is exactly the same way as we ran this other debate poll, which nobody had any problem with us publishing.

“The overall sample we went out to would have been weighted to be representative of the population, including by past vote. So we would have had enough Lab / Con voters etc.

“I don’t remember this being the case, nor do I recall it being mentioned, but 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.

“Either way, 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.”

The 2017 debate was partly notable because Theresa May refused to take part, instead, she was represented by Amber Rudd, whose father had died just two days early. 

Alongside, were the SNP's Angus Robertson, Caroline Lucas from the Greens, Leanne Wood from Plaid Cymru, Ukip’s Paul Nuttall, and Tim Farron from the Lib Dems.

Much of the debate became about Ms May's reluctance to take part.