Allegations against British soldiers who served in the conflict -- and elsewhere around the world -- have dogged the government and military.

But in June last year, an independent investigator looking into claims of war crimes between 2003 and 2009 said all but one of the thousands of complaints had been dropped.

In a written statement to parliament, Wallace said 178 allegations had been formally pursued through 55 separate investigations, but no soldiers had been prosecuted.

In all, 1,291 allegations were assessed since July 2017 and the body responsible, the Service Police Legacy Investigations (SPLI), had "officially closed its doors".

"The vast majority of the more than 140,000 members of our armed forces who served in Iraq did so honourably," Wallace said.

The SPLI was set up to replace the Iraq Historic Allegations Team after a lawyer who had submitted a slew of cases was struck off for misconduct and dishonesty.

Wallace said some allegations were "credible" but others were not, and investigating them all posed a "significant challenge", including in collecting evidence.

"Not all allegations and claims were spurious, otherwise investigations would not have proceeded beyond initial examination and no claims for compensation would have been paid," he added.

"It is sadly clear, from all the investigations the UK conducted, that some shocking and shameful incidents did happen in Iraq.

"We recognise that there were four convictions of UK military personnel for offences in Iraq, including offences of assault and inhuman treatment.

"The government's position is clear -- we deplore and condemn all such incidents."

In February 2005, three soldiers were jailed for between 20 weeks and two years by a court martial for abusing Iraqi civilians at a camp near Basra in southern Iraq in 2003.

In 2007, a soldier was jailed for a year in connection with the death of Iraqi hotel receptionist Baha Mousa, who was beaten while held in custody by British troops in 2003.

The Ministry of Defence has paid out a total of more than pound20 million ($28 million, 24 million euros) in compensation settlements for abuse claims from Iraqi nationals.

Wallace said: "I apologise unreservedly to all those who suffered treatment at the hands of UK forces, which was unacceptable."