A rally by the Coalition for Marriage, the campaign group leading the opposition to equal marriage rights for same-sex couples in the UK, is to take place on Monday 8 October at next month’s Conservative Party Conference in Birmingham.

According to the Daily Mail columnist Andrew Pierce, the rally is being staged at Birmingham City Hall, which has a capacity for 900 people and has already been described as a “sellout” event with “hundreds more on the waiting list”.

Anti-equal marriage figureheads such as former Tory MP Ann Widdecombe and Lord Carey, the ex-Archbishop of Canterbury, are expected to make speeches at the rally.

Earlier this year, Ms Widdecombe called for a referendum on equal marriage. She has also previously backed the right of therapists to offer so-called ‘gay cure’ treatments to clients who want to become straight.

In February, Lord Carey described the coalition’s policy on equal marriage as amounting to “one of the greatest political power grabs in history”.

Mr Pierce claims the event will “overshadow” Chancellor George Osborne’s conference speech on the same day and has received strong media interest.

At last year’s conference David Cameron memorably urged Tory delegates to unite around equal marriage in his keynote speech by saying:

“I don’t support gay marriage in spite of being a Conservative. I support gay marriage because I am a Conservative.”

Although he received rapturous applause, several delegates were seen to leave their seats in disgust.