News that President Obama had decided to end military trials at Guantanamo Bay broke just as I was on my way to see Britain’s new military prosecutor, providing me with a perfect starting point for my interview.

But it is very difficult to imagine Bruce Houlder QC acting as judge, jury and executioner – the charge levelled against the so-called military commissions that have been processing suspected terrorists at the US base in Cuba.

For one thing, Houlder, 61, is a civilian. Since his appointment last year as the first Director of Service Prosecutions, the former chairman of the Criminal Bar Association has had a Boy’s Own Paper introduction to military life: more than six months of planes and ships, squaddies and officers, Iraq and Afghanistan. No civilian has ever enjoyed such a high-level induction.

Despite having picked up a military turn of phrase, he insists he has not gone native; nor was that ever the intention. You need to understand military procedures before you can decide whether service personnel have been criminally negligent, he explains.

‘Take the example of a British aircraft that has brought down fire upon friendly forces. Someone has failed to make a proper identification of the target.’

A ‘blue-on-blue’ incident like this could be the fault of an airman. Or perhaps the responsibility of someone on the ground directing fire. Or neither of them.

‘I have been quite astonished about how concerned our troops are to see that they make decisions which are verifiable and justifiable, not just on purely legal grounds but also on moral grounds,’ Houlder tells me.

Which brings us back to the Americans. ‘It comes as no surprise that President Obama has decided to move on from Guantanamo,’ he says, recalling the president’s election pledge. ‘We have a military justice system which is, in some ways, different from the justice system in the US. It is no part of my wish even to appear to criticise their justice system.

‘But we have subscribed to the European Convention on Human Rights. Our military justice system has been subjected to scrutiny, not only in the highest court in this country but also in Europe. Changes have been made to our criminal justice system as a result, which we might expect to see developed in the thinking of those in the US.

‘The British government has recognised for some time that the rule of law applies to protect those in the power of the executive, and the proper role of the lawyer is to stand between the executive and the individual against abuse of that power.’

Although, like other chief prosecutors, he is subject to the ‘superintendence’ of the Attorney General, Houlder and his team of service prosecutors are free from the military chain of command. Soldiers, sailors and airmen have the right to a fair hearing. Legal aid is available to pay defence lawyers. Civilian judges and civilian counsel are brought in for the most serious cases.

But the ‘jury’ at a court martial is still made up of service personnel, I point out.

True, he says, but service personnel are more likely to trust a military panel. And jurors who think that the Iraq war was illegal might be less willing to deliver a fair verdict on those taking part in it.

That works both ways. In the Baha Mousa court martial two years ago, defendants accused of abusing Iraqi civilians were acquitted of all the offences they had denied. One significant aspect of the case was the ‘wall of silence’ from some witnesses.

Quoting from a report last year by Brigadier Robert Aitken, Houlder says this is not unique to the military, though perhaps exacerbated in an organisation that trains its people in the virtues of loyalty. ‘The challenge is to educate our people to understand that lying to the service police, or having "selective memory loss" in court in order to protect other members of their unit, are not forms of loyalty but rather a lack of integrity.’

Contrary to press reports, the acquittal of soldiers and officers accused of beating Baha Mousa to death in 2003 was not the reason why the three service prosecutors have now been replaced by a single Director of Service Prosecutions, who may be either an officer or a civilian. It dates back to the strategic defence review of 1998, which recognised that the armed forces are increasingly deployed on joint operations.

That, in turn, led to the Armed Forces Act 2006, which replaces the three separate systems of service law with a single, harmonised structure governing all members of the armed forces. It is a huge undertaking, and the need for training has meant that it will not be fully implemented until October.

Section 382 of the 2006 act, incidentally, abolishes Britain’s armed forces from the end of 2011 – unless, of course, a new Armed Forces Act is passed that year, as I have every confidence it will be. The Bill of Rights 1688 provides that the raising of a standing army is against the law unless Parliament consents to it.

It is for this reason that Houlder can tell me – rather proudly, I thought – that there is no such thing as martial law in Britain. Military personnel are certainly subject to laws that do not govern those without links to the armed services, but all service law is subject to renewal by Parliament.

Quite a contrast, then, with the US – where it turns out that the president can end military commissions simply by signing an executive order.