Former Conservative MP Ann Widdecombe says David Cameron’s decision to press ahead with equal marriage explains last month’s Tory defeat in the Eastleigh by-election.

Writing in her Express newspaper column, she said the prime minister had failed to listen to his party and warned that his re-election prospects could be doomed.

“Sorry David but it is you, not your party, that has to change if you are to be PM after 2015. Gay marriage has played an enormous role in all this but you wouldn’t listen – you brushed off your MPs, who were trying to tell you that their supporters were leaving, with the words ‘it’s a free vote’.

The staunchly anti-gay marriage opponent said: “They tried to tell you that no matter how they voted supporters would leave because the Conservatives were introducing the measure – and now Eastleigh has made the point for them – but you wouldn’t listen.”

In last month’s Eastleigh by-election, the Conservative Party – who fielded a candidate opposed to the party’s official policy on equal marriage – came third behind the anti-equal marriage UK Independence Party.

Liberal Democrat Mike Thornton, a supporter of marriage equality, retained the seat for his party on a reduced majority.

In February, MPs voted in favour of the Marriage (Same-Sex Couples) Bill by 400 to 175, a majority of 225.

136 Tories who voted against the bill - it is now receiving further parliamentary scrutiny before a third reading by MPs and House of Lords approval.

In the same month, Ms Widdecombe urged British Christian opponents of equal marriage to stage street protests – something which has already become synonymous with the equal marriage debate in France.