UKIP MEP Roger Helmer, who continues to fend off criticism over his views on homosexuality is likely to come second in Thursday’s by-election, a poll by Lord Ashcroft suggests.

The Conservative peer released the poll on Monday evening and said: “The Conservatives are on course to hold onto Newark in the by-election on Thursday, according to a poll I have conducted in the constituency. I found the Tories on 42%, with UKIP second on 27% and Labour third on 20%.”

Lord Ashcroft suggested that support for Mr Helmer had been influenced by disapproval with the main three Westminster parties. He said: “Seven in ten of those planning to vote for Roger Helmer on Thursday say they are making a general protest to show they are unhappy with all the parties; only 16% of them say this was not a factor.”

Lord Ashcroft added: “More than six in ten UKIP supporters say they were sending a message that they were unhappy with their usual party – more than twice the proportion of Lib Dem voters (and three times the proportion of Labour voters) saying the same.”

Earlier on Monday, Mr Helmer accused The Mail on Sunday of trying to “influence” the result of Thursday’s by-election, after it published an interview featuring his comments about sexual orientation.

Mr Helmer said: “Let’s be clear: I have never said that homosexuality is ‘an illness’, or that it can be ‘cured’.

“I have never asserted that homosexuals can be ‘turned’.  I have never advocated ‘gay cures’.

“In particular I would vehemently oppose any move to offer ‘gay cures’ on the NHS.

“No treatment should be offered on the NHS unless it is of proven clinical efficacy and demonstrable cost-effectiveness.

“I am not aware of any proposal to offer ‘gay cures’ on the NHS – this appears to be a figment of your imagination. But if there were any such proposal, I should oppose it robustly.

“Your suggestion that I ‘called for gay cures on the NHS’ is a downright and preposterous lie, and a deliberate attempt to damage my reputation.”

Roger Helmer was quoted by The Mail on Sunday of having suggested the NHS should offer “cures” for people who are gay.

He previously said the public should be able to openly dislike gay people.

He also claimed homosexuality is not a lifestyle worthy of respect, and that the media are “obsessed” with sexuality.

UKIP leader Nigel Farage attempted to defend Mr Helmer from accusations of homophobia, claiming that “most” over-70s feel uncomfortable about gays.