The low thump, thump, thump, was unmistakable. It was the sound of the Thompson machine gun, a chunky low-velocity weapon.

We all knew it was the IRA's weapon of choice. They liked its macho feel, and had used it on us a couple of weeks earlier when we were patrolling on the nearby Lonemoor Road.

But they had not hit any soldiers that day; they'd hit and injured a 12-year-old girl. 

The sound this time came from somewhere near the Rossville Flats in the Bogside, a nationalist area of Londonderry and a known stronghold of the IRA.

I was standing looking down on the Bogside when I heard it, with Sgt Garrett, my second-in-command in the Coldstream Guards. I asked him to note down the time  -  4pm on January 30, 1972, and then we moved rapidly down the hill towards the sound of the gunfire.

The Army was returning fire now, and the fight was growing in intensity. Not many hours afterwards, 13 men lay dead, seven of them teenagers. Another man was to die four-and-a-half months later.

What happened on Bloody Sunday was a terrible thing, not just for the affected civilians, but also for the Army.

Today the actions of the soldiers who returned fire against the IRA that day will almost certainly be declared by Lord Saville to have been unlawful and, 38 years after the event, this will increase pressure for their prosecution.

The killings may or may not have been unlawful  -  but it is my firm view that it is not possible to judge with any certainty after an interval of more than 30 years whether they were or not.

Furthermore, the £190million expense of this inquiry is nothing less than obscene when British soldiers have been dying in Iraq and Afghanistan daily for want of vital equipment and cuts in the defence budget.

But what I find perhaps most distasteful about this 12-year-long inquiry is that the role of British soldiers in Northern Ireland has been brushed aside for the sake of political expediency.

The truth is that peace was brought to the Province not by Prime Minister Blair, kowtowing to former terrorists such as Gerry Adams and Martin McGuinness.

It came to Northern Ireland as a result of the courage of the British Army, the Ulster Defence Regiment, the Royal Ulster Constabulary and the intelligence services.

By the time Blair offered this inquiry as a sop to Republicans, the IRA had already been militarily defeated by the very soldiers whose reputation he knew it would undermine.

The events of Bloody Sunday were terrifying, fast-moving and chaotic. But as I told the inquiry when called as a witness, there is one thing of which I am absolutely certain.

It was the IRA who started the firing with the Thompson machine gun  -  and, inflammatory though it may sound, I believe they started firing with the express intention of causing civilian deaths.

The security forces' policy was to contain the nationalist civilian protest planned that day behind steel barriers in the Bogside  -  to prevent them from entering the Protestant area of the city. The Army was on one side of the barriers, the protest on the other.

Brigade orders were that the Army should not enter the Bogside  -  for it was known through intelligence sources that the IRA intended to create a bloodbath by drawing the security forces into a firefight with their gunmen in the middle of the civil rights march.

But when I and my second-in-command got down there, we were astonished to find that the barricades had been drawn aside and the paras were moving through into the Bogside, exchanging fire with the IRA gunmen who mostly seemed to be firing from the blocks of flats facing us.

I asked one of the platoon commanders why they had ignored orders.

He told me, above the increasing sound of firing and the screaming from the scattering crowds in front of us, that they had been told to do so by the Commander Land Forces.

It was rumoured that the commander had been irritated by the stones and nail bombs that were being thrown by some of the crowd and had decided to overrule the brigade order and told the paras to arrest the troublemakers. It was a disastrous decision.

I soon found myself taking cover beside a paratrooper who was lying in a gutter by the corner of a building, carefully firing up at the opposite blocks of flats.

When I asked him what he was firing at, he pointed at some crouched figures running along the balconies of the flats. I could see that at least one of them was carrying a rifle.

As I lay in the gutter, I could see bullets hitting the wall of the building above me. There was no doubt that the IRA gunmen were firing from their positions on the galleries of the flats opposite, where I was taking cover.

In my view, it is entirely possible that they could have been responsible for some of the civilian deaths, shooting from on high down into the streets below where the crowd was trying to escape from the killing zone.

But it was absolutely clear that in exchanging fire with the terrorists, the British Army had fallen into the trap laid for them by the IRA, who had set out that day to commit murder and mayhem, caring nothing for the lives of their own republican supporters.

Indeed, I believe it was their specific aim to get as many people killed as possible. For the deaths would serve as a ruthlessly cynical recruiting tool. As the news of the dead in Londonderry that day spread around the world, the result was much the same as Irish people everywhere rallied to the nationalist cause.

In Northern Ireland, in the Irish Republic and in the U.S., thousands of young men and women joined the IRA.

The people of Northern Ireland and the British Army have already paid a high price for what happened on Bloody Sunday, for the consequence of the decision to move the barricades and exchange fire with the terrorists was to heighten and prolong the conflict, probably by decades, with massive loss of life, suffering and destruction.

The decision to hold the Saville Inquiry has been little more than a grotesquely expensive exercise in propaganda, designed by Blair to bring the IRA further into the political process.

But as I have said, the IRA had already been militarily defeated. They had been forced into taking the political route only because they had no further military options to pursue.

How ironic now that the soldiers who brought peace to Northern Ireland are likely to be treated as criminals as a result of this inquiry, while former terrorists such as McGuinness and Adams  -  who did everything to prevent peace  -  are feted in their roles as ministers.

Nor should the effect of the Saville Inquiry on the British soldiers fighting today in Afghanistan be underestimated. Some will be the sons and even grandsons of those being accused of unlawful killing.

Even if they are not, they will be asking themselves whether each time they open fire on the Taliban, they might not, in some distant future inquiry, be asked to justify their actions. This is no way to go to war.

If anyone should be the subject of a judicial process, it is Tony Blair. He should be held to account for his actions in launching the disastrous, costly and unnecessary war in Iraq.

Meanwhile, it will be the British Army and people who bear the cost of this equally disastrous, costly and unnecessary inquiry.

● General Sir Michael Rose is the former Head of UN Troops in Bosnia