A law firm acting for Iraqi civilians who allege unlawful killing and ill-treatment by British forces "misled the court" and failed to observe "essential ethical standards" in one specific case, the High Court has ruled.
A judge made his finding while deciding on the extent of the Government's obligations to investigate hundreds of allegations after the Iraq war
Mr Justice Leggatt, sitting in London, said one of the claims dating from 2003 to 2009 involved a 13-year-old boy fatally injured by an explosion in Haritha, near Basra.
The father of Jaafar Majeed Muhyi applied for judicial review of a Ministry of Defence decision not to hold an "inquisitorial" inquiry into his son's death in May 2003.
The judge said a cause for concern was that when a witness statement was obtained from Mr Muhyi in 2013 for a civil damages claim, Public Interest Lawyers (PIL) failed to note an inconsistency between his evidence and the allegation on which the judicial review application was based.
The father's original evidence was that Jaafar's injuries occurred when he was playing in the street and a previously unexploded munition blew up in his face.
But his new witness statement for the civil damages claim said the boy was killed "by a bomb dropped from a helicopter".
The judge said PIL failed to note the inconsistency. As a result time was spent by the Iraq Historic Allegations Team (IHAT) examining an allegation of failure by British soldiers to clear unexploded cluster bombs when the allegation was no longer being made - "assuming that it had ever been made".
The judge said a second more serious cause for concern was that, at the start of July 2015, one of the claimant's team of four counsel pointed out to PIL that the allegation made in their client's most recent, and only signed, witness statement "was that Jaafar was killed by a bomb dropped from a helicopter".
That allegation was quite different from the allegation that the 13-year-old was killed as a result of playing with an unexploded cluster munition.
The judge said "no responsible lawyer aware of the 2013 witness statement and conscious of their duties to their client and the court" would have felt able to advance the original allegation as the current case without first raising the inconsistency with Mr Muhyi and receiving instructions from him.
"That, however, is exactly what the claimant's legal team did. Amended grounds for judicial review, signed by all four counsel, were served which advanced a positive case that Jaafar was killed as a result of playing with an unexploded cluster munition."
The explanation given was that the deadline for service of amended grounds for judicial review was imminent and it was not possible in the time available to contact Mr Muhyi to confirm whether his 2013 witness statement was correct.
The judge said that could not justify putting forward a case that was inconsistent with the client's most recent evidence - "while concealing that fact from the other party to the litigation (MoD) and the court".
By acting as they did, Mr Muhyi's representatives "misled the court and thereby obtained permission to proceed with the claim".
They also caused the MoD to incur "the trouble and expense of preparing evidence and argument in response to a claim for which there was no proper basis".
It was not a brief aberration quickly corrected, but persisted over three months before the true position was disclosed in early October 2015, the judge said.
PIL has submitted hundreds of allegations of misconduct and unlawful killing by British troops to IHAT, many of which have given rise to legal battles in the courts.
The judge said he had been "immensely impressed and grateful" to the law firm and counsel instructed by them "for the dedicated and responsible way they have represented the interests of their clients and ensured that important issues are raised and argued".
But he added: "Against that background, it is all the more disappointing to encounter in their conduct of this claim such a serious failure to observe essential ethical standards."