Two High Court judges today blocked attempts to force a public inquiry into the killing of 24 Malaysian rubber plantation workers by British troops more than 60 years ago.
Victims' relatives described the shootings at Batang Kali, Malaya, in December 1948 as a "massacre" and judges said allegations against members of the Scots Guards were "as serious as it is possible to make".
But Sir John Thomas - president of the Queen's Bench Division of the High Court, who sat with Mr Justice Treacy - said it would be "very difficult at this point in time" to establish whether the shootings were "deliberate executions".
Judges said the cost of an inquiry would be "materially greater" than £1 million and said it was "very questionable" whether "much can be learnt".
British soldiers were conducting operations against communist insurgents during the "Malayan Emergency" when the plantation workers were killed, judges heard.
Relatives said there was enough evidence to justify an official investigation and asked judges to overturn a Government decision not to hold an inquiry.
Foreign Secretary William Hague and Defence Secretary Philip Hammond opposed the relatives' application, arguing that the decision not to hold an inquiry was lawful.
Judges today ruled in the Government's favour following a hearing in London in May.
Relatives said they would appeal.
Sir John, in a written ruling handed down at a hearing in London, said: "The first matter in relation to the purpose of inquiry is to consider whether it can establish the facts.
"There are obviously enormous difficulties in conducting an inquiry into a matter that happened over 63 years ago. Most of the contemporary documents are missing and most of those who were engaged are dead."
He added: "All in all, it would appear to be very difficult at this point in time to establish definitively whether the men were shot trying to escape or whether these were deliberate executions.
"Nor, in our view, would it be any easier to determine whether the use of force was reasonable or proportionate."
Sir John said decisions taken by Mr Hague and Mr Hammond not to set up an inquiry were "not unreasonable".
Solicitor John Halford, who represents victims' families, said after today's hearing, that relatives would appeal.
Mr Halford, from law firm Bindmans, added: "The survivors and families of the Batang Kali massacre will continue to pursue legal action."