THE resignation of Cardinal Keith O'Brien as Archbishop of St Andrews and Edinburgh following allegations that he behaved inappropriately towards three priests and one former priest puts the issue of sexual abuse at the heart of the Catholic Church in the week when cardinals gather at the Vatican to elect the new Pope.

Cardinal O'Brien denies the claims, which date back to 1980. Despite his decision not to attend the conclave because he wants to avoid a focus on him when attention should be concentrated on Pope Benedict XVI and his successor, how the church handles clerical abuse must be a key consideration.

Much will be read into the timing of these claims. In particular, since they date back more than 30 years, some will question why they are surfacing now. One of those alleging unwanted contact and inappropriate behaviour has said that he resigned from the priesthood when Keith O'Brien was appointed a bishop because he would always have power over him. That is an indication of how much the culture within the church has changed from one of absolute hierarchical power over the last 30 years. That it is now possible for priests to use the Vatican's diplomatic service to raise a complaint about abuse by a superior directly with Rome is a revolution that owes much to belated admission of child sex abuse on the part of the church.

That these complaints are now being investigated, and the fact that Pope Benedict announced Cardinal O'Brien's resignation is to take immediate effect, show a new recognition of the need for swift action. This is progress, or at least an understanding that the reputation of the church depends on dealing with abuse seriously and that concealment compounds the problem.

Yet some senior figures have remained obdurate. Cardinal Roger Mahony, archbishop emeritus in Los Angeles, was shown to have protected priests when files relating to 120 who were accused of child sex abuse were ordered to be released. Only last week, the archbishop of New York, Cardinal Timothy Dolan, was questioned about when he knew of the abuse of children in his former archdiocese of Milwaukee. Cardinal Sean Brady, the primate of All Ireland, has faced calls to resign over his failure in the 1970s to report a serial abuser. The conclave to choose the successor to Pope Benedict will be controversial for a number of reasons but seems likely to be overshadowed by sexual scandal.

Add to this the continuing speculation about Pope Benedict's resignation being prompted by claims that one of the powerful factions within the church is a network of homosexual priests and it is clear the next Pope will face the immediate and enormous challenge of restoring confidence in the integrity of the Catholic church and the probity of the priesthood.

Only last weekend, as Cardinal O'Brien was preparing to go to Rome, we welcomed his suggestion that it was time to reconsider the requirement for Catholic priests to be celibate. But that intervention has been all but forgotten by his resignation, which has contributed to plunging the church into its biggest crisis in 500 years.