A front page story in The Sun that claimed one-in five British Muslims had sympathy with jihadis who go to fight for Islamic State (Isis) in Syria has provoked a record number of complaints, Britain's press watchdog has confirmed.

The Independent Press Standards Organisation (IPSO) received more than 1,200 complaints about the story in just over 24 hours, eclipsing the 400 it received in the weeks following a Katie Hopkins column, also in The Sun, that referred to migrants fleeing Syria and Africa for Europe as "cockroaches". It also surpassed the 300 received by Ipso after the Daily Mail published a cartoon that showed rats running beneath the feet of fleeing refugees, a spokesman told IBTimes UK on 24 November.

It has emerged that The Sun's claim was based on a survey commissioned after the Paris terror attacks, in which IS-affiliated gunmen killed 130 people in the French capital. The survey, by polling firm Survation, claimed that as many as 19% of British Muslims had some sympathy with Britons who had travelled to Syria to fight against the regime of Bashar al-Assad.

Critics have since questioned the accuracy of the survey after claims that pollsters distinguished between Muslims and non-Muslims by using only their names and that The Sun's usual polling company, YouGov, had declined to carry out the survey as it was too complex and expensive to do in the timeframe given.

Others cited an earlier survey by Sky News that suggested as many as 30% of non-Muslims had expressed sympathy for young Muslims fighting in Syria – far more than the almost 20% of Muslims claimed by The Sun.

The question pollsters asked referenced "young Muslims who leave the UK to join fighters in Syria" and whether the responder had sympathy for them with no reference to IS or jihadis, despite the fact that the latter was used in the headline. There are dozens of militias currently fighting in Syria, many of them Islamist but others Christian and Kurdish and some backed by Europe, the US and other non-Muslim states.

Shuja Shafi, secretary general of the Muslim Council of Britain, also criticised the story on Tuesday, arguing that many Muslims would find the poll hard to believe.

"The vast majority of the almost three million British Muslims abhor terrorism," he said. "Poll after poll attest to this, as do the many surveys showing how almost all British Muslims would report someone from the Muslim community to the police, if they knew they were planning an act of violence."

The Sun defended its story in an editorial on Tuesday, arguing that the attacks were being made by the "political left" and that surveys by both the BBC and Sky News following the Charlie Hebdo massacre showed similar results.

"All three polls reveal an undeniable truth: Among British Muslims, a minority – but a substantial one – appear sympathetic to a death cult which is among the most evil in history. Once we all accept that, Britain is better placed to tackle it," it said.