Gay rights groups have 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.

On Monday, the Scottish Catholic Church said Pope Benedict XVI had accepted the resignation of Cardinal Keith O’Brien as leader.

The cardinal has been an outspoken opponent of plans to legalise same-sex marriage in the UK.

In March 2012, he said it was a “grotesque subversion of a universally accepted human right,” suggested that marriage equality would lead to three-way marriages – and was akin to legalising slavery.

The 74-year-old will no longer take part in the election for a successor to the Pope – leaving Britain unrepresented in the election.

Pope Benedict XVI, who previously referred to gay people as a “defection of human nature”, officially stands down on Thursday.

He announced his resignation earlier this month due to failing health.

Stonewall Chief Executive Ben Summerskill reacted to the news of Cardinal O’Brien’s resignation by saying: “We trust there will be a full investigation into the serious allegations made against Cardinal Keith O’Brien. We hope that his successor will show a little more Christian charity towards openly gay people than the cardinal did himself.”

Last November, Cardinal O’Brien was named ‘Bigot of the Year’ by Stonewall due to his staunch opposition to marriage equality.

Tom French, from Scotland’s Equality Network said: “It would be inappropriate for us to comment on the allegations made against Cardinal O’Brien. Of course we hope that the Catholic Church in Scotland will use the opportunity new leadership brings to reassess its opposition to lesbian, gay, bisexual and transgender (LGBT) equality.

“The Catholic Church does a huge amount of good work on issues like poverty, and it’s a shame that this important work is so often overshadowed by its position on issues of sexuality.”

In a statement on Monday, Cardinal O’Brien gave greater details of his resignation, which had been accelerated by the events of the past 48 hours.

He said: “For any good I have been able to do, I thank God. For any failures, I apologise to all whom I have offended.”

The full statement read:

Approaching the age of 75 and at times in indifferent health, I tendered my resignation as Archbishop of Saint Andrews and Edinburgh to Pope Benedict XVI some months ago. I was happy to know that he accepted my resignation ‘nunc pro tunc’ – (now – but to take effect later) on 13 November 2012.

The Holy Father has now decided that my resignation will take effect today, 25 February 2013, and that he will appoint an Apostolic Administrator to govern the Archdiocese in my place until my successor as Archbishop is appointed. In the meantime I will give every assistance to the Apostolic Administrator and to our new Archbishop, once he is appointed, as I prepare to move into retirement.

I have valued the opportunity of serving the people of Scotland and overseas in various ways since becoming a priest. Looking back over my years of ministry: For any good I have been able to do, I thank God. For any failures, I apologise to all whom I have offended.

I thank Pope Benedict XVI for his kindness and courtesy to me and on my own behalf and on behalf of the people of Scotland, I wish him a long and happy retirement. I also ask God’s blessing on my brother Cardinals who will soon gather in Rome to elect his successor. I will not join them for this Conclave in person. I do not wish media attention in Rome to be focused on me – but rather on Pope Benedict XVI and on his successor. However, I will pray with them and for them that, enlightened by the Holy Spirit, they will make the correct choice for the future good of the Church.

May God who has blessed me so often in my ministry continue to bless and help me in the years which remain for me on earth and may he shower his blessings on all the peoples of Scotland especially those I was privileged to serve in a special way in the Archdiocese of Saint Andrews and Edinburgh.