Britain's most senior Roman Catholic cleric, a cardinal expected to take part in the conclave to choose the next pope, rejected allegations on Sunday that he had behaved in an "inappropriate" way with other priests.

The Observer newspaper said Cardinal Keith O'Brien, 74, the archbishop of St. Andrews and Edinburgh, who is known for outspoken views on homosexuality, had been reported to the Vatican over allegations of inappropriate behaviour stretching back 30 years.

 "Cardinal O'Brien contests these claims and is taking legal advice," a spokesman for the cardinal said.

Three priests and a former priest, from a Scottish diocese, have complained to the Vatican and demanded O'Brien's immediate resignation, the newspaper said, adding that they wanted the conclave to choose Pope Benedict's successor to be "clean".

The Observer gave little detail on the allegations but said one complainant had said O'Brien made an inappropriate approach after night prayers. Another priest complained of unwanted behaviour by O'Brien after a late-night drinking session.

Last week, O'Brien advocated allowing Catholic priests to marry as many found it difficult to cope with celibacy.

His comments last year labelling gay marriage a "grotesque subversion" landed him with a "Bigot of the Year" award from gay rights group Stonewall.

The Catholic Church's handling of the sexual abuse of children and others by priests has dogged the papacy of Benedict, who is due to step down on Thursday after becoming the first pope in centuries to choose to resign.

The next leader of the world's 1.2 billion Catholics will be chosen by 117 cardinals in the Vatican's Sistine Chapel.

Almost 10,000 people have signed a petition urging a U.S. cardinal not to take part in selecting the next pope, saying to do so would insult victims of sexual abuse by priests committed while he was Archbishop of Los Angeles from 1985 to 2011.