The Stevens report was just one more exercise in self-flagellation

It is hard for liberal democracies to brace themselves to take the necessary steps to defeat terrorism. In Ulster, the IRA has spent three decades exploiting this and trying to make the counter-terrorists' task impossible. Throughout those years, insisting that they were at war, the Provos demanded every right normally accorded to armies in the field – except the right to be fought. When it came to measures against them, they and their supporters ruthlessly exploited all the opportunities granted to them by the rule of the law which they were trying to destroy.

There was no way of trying to defeat the IRA without moral hazard. In dealing with the Provos, the security forces' most important weapon was intelligence, gathered through informers. But relationships with informers inevitably lead their handlers into grey areas.

Let us assume that the security services have a highly placed source within the IRA. He tells them of plans to murder cabinet ministers or members of the Royal Family – or to blast a city centre with a huge explosion. He also reveals details of a forthcoming bank raid. Those in charge of him know that if every operation in which he is involved goes wrong, suspicion will quickly be aroused. At best, he will succeed in fleeing for his life; at worst, he could suffer a horrible death. Whatever happens, there will no longer be an informant. So they decide to let the bank raid proceed; the only possible decision.

Yet it would also be an illegal one. There is no law which grants the security services immunity from being prosecuted as accessories should they fail to disclose foreknowledge of an intended crime. So almost anyone involved in running informers in Ulster was in a position where it would be his duty to break the law.

There may have been occasions when those breaches of the law became very grey. Sooner or later, someone will rewrite the history of the Second World War in the light of Enigma. This will reveal instances in which counter-measures to thwart small German operations were not taken, in order to avoid the risk of alerting the Germans to our code-breakers' successes. It was not worth compromising Enigma to save mere handfuls of British lives.

There were almost certainly parallels in Ulster. There are reports that in order to protect Stakeknife, the codename for the most important informer within the IRA, lesser informers were sacrificed. They may not have been the only sacrifice. A major IRA operation is in prospect; it is vital that it should be frustrated. The indispensable informer also reveals that an RUC man is about to be murdered. Is it worth risking the big game in order to save one policeman's life? I am glad that I have never had to take a decision like that. We should all be glad that there were brave and conscientious men to run security policy in Ulster and to take such decisions. In so doing, they saved large numbers of lives. They deserve our gratitude.

That is not the tenor of the Stevens Report. It would appear that Sir John Stevens has uncovered instances where grey did turn into black, especially as regards collusion between the security services and the Protestant paramilitaries. Yet even there, there is a case for the defence.

The Protestant paramilitaries were in business to kill. They were also a pretty crude lot; Protestant terrorists tend to have more tattoos than O-Levels. This often manifested itself in the choice of targets. They were inclined to bump off inebriated Catholic barmen who had merely taken a wrong turning on the way home. So one can understand the inclination to guide their homicidal instincts away from the innocent and towards the guilty.

According to Sean O'Callaghan, himself for many years a highly placed informer within the IRA, Pat Finucane was one of the guilty. Finucane, he claimed, was a senior Provo who used his privileges as a lawyer to liaise between the IRA and its operatives in custody. He was only innocent in the sense that no case had been proved against him in a court of law. It is also possible that the agents who may have been complicit in Finucane's death were the same ones who intervened to foil the assassination attempt on Gerry Adams. The security services' willingness to save Adams' life does not suggest that they were out of control.

There were problems. Back in the late Eighties, difficulties arose with intelligence co-ordination in Ulster because too many organisations were involved. The RUC Special Branch, the mainland Special Branch, the Army, MI5 and – for a time – MI6 were all operating. This inevitably led to departmental rivalries and conflicts of modus operandi.

Policemen are trained to gather evidence of a crime so as to secure convictions in court. Intelligence officers set out to build up as complete a picture as possible of enemy groups which threaten the security of the UK, and would always oppose any premature arrests which might jeopardise more important objectives. Equally, the absence of clear lines of co-ordination and command might have encouraged individual intelligence officers to go too far.

It must have been infuriating to watch IRA murderers who were acting with impunity because of the constraints of the legal system. One can understand why some intelligence officers might have been tempted to find an extra-legal solution to the law's inadequacies. Such temptations ought, of course, to have been resisted. Someone senior should have been scrutinising intelligence employees and asking themselves whether X or Y had now spent too long wrestling with the frustrations of Ulster and ought to be redeployed, in his own interests as well as HMG's.

There was not enough of that, so excesses occurred. But these ought to be put into context. For almost 30 years the Provisional IRA was responsible for a campaign of terror. Thousands of innocent people were murdered; tens of thousands of lives were blighted by injury and grief. Throughout this period, the British Government, the security services, the armed forces and the police behaved with a restraint which few if any other nations could have equalled. It could easily be argued that at times the restraint was excessive. There is no argument for national self-flagellation in response to the occasional breaches of restraint. Nor is there any sound argument for further inquiries.

As it is, the Saville Inquiry is spending hundreds of millions of pounds establishing what everyone already knows: that blunders were committed on Bloody Sunday. As for the Stevens inquiry, an internal review within the security services would have been sufficient to discover what if anything had gone wrong and what lessons should be learned for future operations. Sir John should now be invited to concentrate on his real job: providing London with a reliable police force. Security is safe with the security services, while the blame for the ills of Ulster is easy to apportion. It lies with the IRA.