Cardinal Keith O’Brien had a long-standing sexual relationship with a man while he was the leader of Scotland’s Catholic Church.

The man, who left the priesthood in the middle of the last decade, confessed to the relationship after complaints of sexual misconduct from other priests had been revealed.

Scottish daily newspaper The Herald reports the man, who has since re-joined the Catholic Church, was known to be in regular telephone contact with O’Brien and was a frequent visitor to his official residence in Edinburgh.

Two of the priests who claim they were abused by O'Brien say they were exasperated by the Cardinal’s double standards when it came to gay rights and marriage equality.

Declaring ‘war’ on plans for same-sex marriage in the country, and likening it to slavery and child abuse, were some of his many comments.

It is thought his statements, such as describing homosexuality as a ‘moral degradation’, were a ‘tipping point’ for those close to him.

On the day O’Brien became a ‘prince of the Church’, he allegedly attempted to grope a priest at a drunken party in Rome.

This complaint, made in September 2012, led to the four others lodging their own complaints with the Vatican.

One senior church figure said that while some fundamentalist Catholic groups had previously linked the priest with O'Brien ‘there were many questions that others were asking about the relationship’.

Another source said: ‘These guys, we now know, were part of an inner circle.

‘In the 30 years since these allegations took place there's been ample time to complain. The Cardinal has had a huge profile for the past decade. But the door wasn't just shut on them, it was bolted in the past 18 months.

‘I believe they wanted to silence O'Brien - as he's about to do another conclave, and make a huge deal of it. As he's retiring, a decision's been taken to go public and take him down.’

Another said: ‘If you're asking me to describe what this is about in one word, it's revenge. I've no doubt the allegations did take place in the 1980s but they've come out to - destroy O'Brien.’

A Catholic Church spokesman said: ‘Some clergy were not in favour of Church efforts to persuade the Scottish Government against same-sex marriage.

‘It is also the case that objections were raised to Cardinal O'Brien's robust rhetoric.

‘A number of complaints about Cardinal O'Brien were passed directly to the Vatican. Whether they were precipitated by his comments on homosexuality is not known, since the detail and nature of the complaints were not shared with the Bishops' Conference of Scotland.’

When O’Brien resigned, he admitted there had been times when his ‘sexual conduct has fallen below the standards expected of me as a priest, archbishop and cardinal’.

'I will now spend the rest of my life in retirement. I will play no further part in the public life of the Catholic Church in Scotland,’ he said.