Sometimes justice can best be done by not enforcing the criminal law

If the homicidal priest had been prosecuted, the whole of Northern Ireland would have been brought to an abyss of sectarian violence

Hindsight makes for easy moral judgement. Thirty years on, Willie Whitelaw's refusal to prosecute Father James Chesney will find few defenders. Most people will be so overcome with revulsion at the thought that a Christian minister of religion could have been involved in such an atrocity that they will condemn rather than reason.

This is an understandable reaction. The attack on the peaceful village of Claudy, in which nine people were killed and a community ripped apart, was not just murder. Although some of the victims were Roman Catholic, it was an attempt at ethnic cleansing which ought to have put the criminals beyond the scope of mercy.

William Whitelaw's decision to extend that scope will be widely interpreted as an enervate concession from a decadent Tory establishment, and the old nicknames may even be revived. His detractors used to call him "Wobblelaw" or "Wetlaw"; Ian Paisley often referred to him as "Willie Whitewash". Perhaps it should have been "Bloodwash". The criticisms are easy to make. There will be widespread indignation – and indeed fury – at his leniency. Yet there is a case to be made for Lord Whitelaw. I believe that he was right.

Back in 1972, the London government was desperately trying to convince itself – and everyone else – that the Ulster problem could be solved by judicious reforms. British ministers were determined to reject the idea that they were confronting a conflict of nationalism, which had been going on for centuries and which by its very nature was irresolvable except by a bloody victory for one or other side after an atrocious civil war. The history of that aspect of Irish affairs had been written by Yeats, in four words: "Great hatred, little room". That was not what Ted Heath, Willie Whitelaw and their other colleagues wished to believe. Who can blame them?

Then a priest commits a foul murder: a crime deserving the full rigour of the law, especially in view of its perpetrator. So what happens if he is prosecuted? Initially, the IRA's cause would be discredited. There would be dismay in Dublin and Boston. The Unionists would have an opportunity to occupy the moral high ground, and their politicians would try to take it, under the shrewd leadership of Brian Faulkner. Five minutes later, however, they would have been washed off that high ground, in a wave of bloodshed by Protestant extremists.

Back in 1972, a large number of Ulster Protestants still believed that most Catholics were closet sympathisers with terrorism, and that they were abetted in this by their clergy. Along comes Father Chesney, and appears to vindicate those prejudices. There would have been mass outrage among Protestants, and in some quarters it would not have found mere linguistic expression. Revenge would have been taken, and many of the victims would have been guiltless. Among them would have been innocent Catholic priests, and once a couple of them had been done to death, Dublin and Belfast would have forgotten all about the innocents of Claudy.

Willie Whitelaw's personal courage was never in doubt. He had a good and decorated war, fighting through northern France with the Guards' Armoured Division which suffered some of the highest British casualties per battalion in the Second World War. Many of those casualties were men in Willie's own battalion, including some of his closest friends. Nor was the refusal to prosecute Father Chesney a weak man's decision. A weak minister would have let the law take its course.

If so, it would have been a bloody course. In 1972, the security position in Ulster was deteriorating rapidly. It was a year which saw the highest ever terrorist casualties in the province plus the suspension of the Stormont parliament. At various moments, the Northern Ireland ministers feared that the situation might be slipping out of control.

It was not surprising that when he was told about Father Chesney, Willie Whitelaw felt obliged to weigh the exigencies of raison d'état against the demands of justice. If the homicidal priest had been prosecuted, the resulting chain of dire events would have resulted in far more than nine innocent deaths. It might even have brought the whole of Northern Ireland to the edge of an abyss of chaos and sectarian violence.

Willie Whitelaw found himself caught between two legal maxims. On one side, there was fiat justitia, ruat coelum: let justice be done, though the heavens fall. On the other, salus populi suprema lex: the supreme law is the safety of the people. Over the centuries, philosophically inclined students of law have had the luxury of debating those alternatives in the seminar rooms of the world's universities, and the argument will go on as long as law is studied. Willie Whitelaw had to work to a tighter timescale. He could not indulge himself in insoluble problems; it was his responsibility to make an urgent choice. So he chose the people's safety.

There are two further aspects to the whole affair, the first of which concerns the British way of government. If the news of the Whitelaw decision had leaked at the time, everything which he most feared would have happened anyway, while he would have been discredited, reviled and forced from office. That he took such a risk is a further tribute to his courage.

Since then, however, such ministerial courage has become even more hazardous, as the number of leaks multiplies. It is not clear that any of today's ministers would dare to make the same decision – because they would be doing so knowing that their good intentions were almost certain to be frustrated by a leak, which would also destroy their own career. In desperate circumstances, ministers cannot always be expected to behave like boy scouts. Yet it may be that the prevalence of leaking has now crippled the decision-making process, so that ministers will feel compelled to claim to be acting morally when they are in fact guilty of cowardice.

The second reflection concerns the Catholic church. Willie Whitelaw was not the only senior figure who put himself in moral hazard over the Chesney affair. So did the Catholic Primate of all Ireland, Cardinal Conway. He was no doubt relieved to avoid the embarrassment of having one of his priests prosecuted for mass murder. Perhaps, however, he was so overcome by relief that he then failed to scrutinise his own conscience and to take steps to ensure that no other Irish Catholic priest would ever be so steeped in blood and sin as James Chesney was. There is no evidence that Cardinal Conway ever tried to learn the lessons of the Claudy affair.

This had other consequences. At the same time as Father Chesney was committing murder in Claudy, large numbers of other Irish Catholic priests were abusing the sacramental authority of their office and the trust of their congregations to indulge in sexual assaults on small boys. But why should a hierarchy which is prepared to tolerate murder draw back from paedophilia? Willie Whitelaw took a hard decision to pervert the law to save lives. Cardinal Conway took an easy way out.