Human rights campaigner Peter Tatchell has reacted to the resignation of Cardinal Keith O’Brien, Britain’s most senior Roman Catholic, who has been accused of inappropriate behaviour with male priests.

Earlier on Monday, Cardinal O’Brien apologised to those he had offended for “failures” during his ministry and announced in a statement that he was standing down as leader of the Scottish Catholic Church.

He will not take part in electing a new pope, leaving Britain unrepresented.

In a statement, Peter Tatchell said: Cardinal O’Brien condemned homosexuality as a grave sin and was a long-time opponent of gay equality.

“He supported homophobic discrimination in law, including the current ban on same-sex marriage.”

Of the allegations – which the cardinal has denied – Mr Tatchell claimed: “In the light of these allegations, his stance looks hypocritical.

“He appears to have preached one thing in public while doing something different in private.

“Several other prominent opponents of equal marriage are guilty of double standards and vulnerable to similar exposure. They include anti-gay clergy and politicians.”

Mr Tatchell claimed: “It is estimated that around 40% of Catholic priests in Britain are gay, which makes the church’s opposition to gay equality so two-faced and absurd.

“Nearly half of all Cardinals worldwide are thought to be gay.”

He added: “Recent revelations in Italy have alleged the existence of a gay mafia within the Vatican, including senior Cardinals and other Vatican officials, and their participation in gay bars, clubs, saunas, chat rooms and escort services.

“The Vatican is shamelessly championing homophobia and the denial of legal equality to gay people, while hosting a hotbed of secret, guilt-ridden clerical homosexuality.”