An ongoing public inquiry into allegations against British soldiers in Iraq has already cost more than £18 million, and is not expected to publish its report until late 2014.
The Al-Sweady Inquiry, looking into claims of unlawful killing and ill-treatment following a battle in May 2004, follows on from an investigation by the Royal Military Police which was judged inadequate by the High Court in 2009.
The expenditure figure of £18.5 million for the current inquiry is from 1 December 2009, and does not include either VAT or the costs for various key witnesses and participants being met by the Ministry of Defence.
The families of Iraqi nationals pushed for a judicial review after it was claimed that Iraqi detainees were murdered at a British camp, and five others were repeatedly mistreated during imprisonment, following a battle near Majar-al-Kabir on 14 and 15 May 2004.
The Battle of Danny Boy, named after a checkpoint near its location north of Basra, involved close-quarters use of bayonets after around a hundred armed insurgents ambushed a patrol of the Argyll and Sutherland Highlanders and the Princess of Wales's Royal Regiment.
Around 50 witnesses have already given evidence about what happened next to the inquiry, which adjourned for the summer on Thursday, and a further 200 statements are to be scheduled for when oral hearings resume in September.
Labour MP Katy Clark today voiced concerns about the length of the process.
She said: "The allegations made by the relatives of those who died in the 'Battle of Danny Boy' along with those who survived the battle are among the most serious to be made against UK armed forces during the whole of the Iraq war.
"While it's right that these are thoroughly investigated, the whole process is taking far too long.
"Those involved have had to wait over nine years already to learn the truth about exactly what happened in May 2004 and may be made to wait a further year before the Al-Sweady Inquiry publishes its findings.
"These costly and lengthy proceedings need to be concluded as swiftly as possible."
Matthew Sinclair, chief executive of the Taxpayers' Alliance, said those responsible for the inquiry should bear in mind who is "picking up the tab".
He said: "Public inquiries are a lengthy and costly process, but the authorities must do far more to keep the bill to taxpayers down."
A spokeswoman for the inquiry said: ""Unlike most public inquiries, the facts at the centre of this case are hotly disputed. Therefore the Inquiry had to set up an investigation to gather together the evidence and identify witnesses.
"The inquiry had to undertake a massive disclosure exercise, involving the approach of over 600 military personnel and around 100 Iraqi witnesses, and the addition of more than 6,000 documents [from the Ministry of Defence].
"We are also investigating events which occurred nine years ago, in another jurisdiction with complex international dimensions. Taken together these factors help explain why the inquiry has taken three years to carefully assemble the evidence."