WHEN very serious allegations about the conduct of British forces abroad go unanswered, it is corrosive both to Britain's international reputation as well as to the morale of the great majority of military personnel, who behave with decency and integrity even in the most trying of circumstances.

So the best that can be said of the al-Sweady inquiry, which finally got under way in London yesterday, is that it is a case of better late than never.

In May 2004 Shia insurgents ambushed vehicles belonging to the Argyll and Sutherland Highlanders north of Basra. Following the incident, known as the battle of Danny Boy, it is alleged that British troops killed some detainees and tortured others. In some cases the death certificates documented signs of torture, such as gouged-out eyes. These are the most serious allegations ever made against British troops in Iraq.

The Royal Military Police (RMP) was asked to investigate these claims, made by some of the surviving detainees and relatives of the dead, including the uncle of Hamid al-Sweady, who died aged 19. The RMP concluded that 20 corpses and nine live captives were brought to the camp. The survivors were released without further injury. None of the survivors was interviewed.

The Ministry of Defence is sticking to this narrative and nothing more would have been heard of the incident had a panel of high court judges not reviewed the handling of this case and accused the MoD of "lamentable" behaviour and "serious breaches" in its duty of candour. Labour's Bob Ainsworth, defence secretary at the time, "consistently and repeatedly failed to comply" with the requirement to disclose documents the claimants were seeking and used public interest immunity certificates to suppress information, the judges concluded.

The current inquiry is still waiting for written evidence from the MoD, including emails relating to a visit by the Red Cross, which is said to have expressed concern about some of the detainees' injuries.

As the head of the inquiry, Sir Thayne Forbes, said yesterday, there is a "stark dispute between the two sides". His task is to decide who is telling the truth. Investigating this matter has already cost taxpayers £15m. Now that figure could treble. The Ministry strenuously denies the allegations. Indeed, not to do so would amount to admitting a conspiracy to bury the truth along with the young Iraqis.

It is damaging and unacceptable that it takes so long to address these matters. Of all the accusations of abuse levelled at British troops in Iraq, only one – into the shocking death in custody of hotel receptionist Baha Mousa – has concluded and only one soldier has been jailed. This is not only morally wrong but self-defeating. It robs the UK of its moral authority to criticise brutality and high-handedness in the army or police in countries such as Zimbabwe, South Africa and Russia.

Bad things happen in the fog of war. Emotions can run high among companies of soldiers, especially when their own mates are being injured or killed. But if things get out of hand, it is essential that there is a prompt, thorough and impartial investigation to back up the claim that "We do things properly here".