Six Red Caps were killed in southern Iraq in June 2003
The government considered a British operation to arrest eight people suspected of killing a group of UK Red Caps in Iraq in 2003, documents show.
Foreign Office documents obtained by the BBC reveal that the plan for unilateral action was later rejected for fear of stoking up controversy.
The six military policemen were killed by an Iraqi mob in Majar al-Kabir.
Families of some of the dead men say they are frustrated by local inaction and have renewed calls for arrests.
The Red Caps were set upon by an estimated 400 Iraqis in a police station in June 2003.
Last February, a court in Baghdad issued arrest warrants for eight suspects.
A year on, nobody has been detained despite pressure from the UK government.
The six Red Caps killed were Sgt Simon Hamilton-Jewell, 41, from Chessington, Surrey; Cpl Russell Aston, 30, from Swadlincote, Derbyshire; Cpl Paul Long, 24, of Tyne and Wear; L/Cpl Benjamin McGowan Hyde, 23, from Northallerton, North Yorkshire; L/Cpl Tom Keys, 20, from Bala, North Wales; and Cpl Simon Miller, 21, from Tyne and Wear.
Families of the dead soldiers say that, when they have asked for unilateral action, they have been told Iraq security forces are required to take the lead.
The families say they are due to meet Defence Secretary Des Browne in a fortnight and will raise the issue again.
Reg Keys, father of Tom Keys, told the BBC the families have experienced "12 months of frustration".
"I will be saying to Mr Browne 'Tell us whether you are going to arrest them, yes or no."
He said if an operation to execute the warrants were to be "effective and professionally run, it has to be British-led".
Simon Miller's father, John, said: "I've been saying for a long time now - what is it about this incident that the MoD and the government and the Iraq government just will not act on.
"It becomes very suspicious. I don't believe it will ever happen."
A Ministry of Defence spokesman said the Baghdad court's arrest warrant had not yet been followed through.
But the UK was applying diplomatic pressure at high levels.
"We do not have the power to put people on trial - we are present in Iraq at its government's request and must respect its sovereignty.
"UK forces are legally allowed to detain persons suspected of committing an offence in Iraq but detainees are handed to Iraqi authorities as soon as is practicable - usually less than eight hours."
An MoD inquiry into the deaths found they could not have been prevented.
In March 2006, a coroner recorded a narrative verdict of unlawful killing.
Nicholas Gardiner said the six men should have been better equipped, but their deaths could not have been avoided.