Human rights campaign group Amnesty International is backing a call for a public inquiry by the families of soldiers found dead at the Deepcut army barracks.
Cheryl James died of gunshot wounds in 1995
The families of four young soldiers - including 18-year-old Cheryl James from north Wales - who died from gunshot wounds at Deepcut barracks in Surrey between 1995 and 2002, will on Wednesday meet MPs who want an independent investigation into the deaths.
Ms James, from Llangollen, was found dead with gunshot wounds at the barracks in 1995.
An army investigation said she had committed suicide, but an inquest recorded an open verdict.
Her case and those of three others found dead in similar circumstances forms part of an ongoing investigation by Surrey Police.
THE DEAD SOLDIERS
Pte Sean Benton, 20, from Hastings, East Sussex
Pte Cheryl James, 18, from Llangollen, north Wales
Pte Geoff Gray, 17, from Seaham, County Durham
Pte James Collinson, 17, from Perth, Scotland
The Ministry of Defence (MoD) has refused to comment until that investigation is complete.
The bereaved families met MPs and representatives of Amnesty International at Westminster on Wednesday to increase pressure on the MoD to allow a public inquiry.
In a statement, Amnesty said the UK Government should establish a full, independent inquiry into non-combatant deaths among members of the UK Armed Forces.
A spokesman said: "Sadly, the manner in which the investigations into the deaths of the four soldiers at Deepcut barracks were conducted has led to a perception that there has been institutional collusion and cover-up of the circumstances surrounding these deaths."
The organisation added that the Royal Military Police's Special Investigation Branch (SIB) conducted the original investigations into all four Deepcut deaths.
Justice must be delivered to these families, but it must also be seen to be delivered
Although the army originally classified all four deaths as "intentional and self inflicted," two of the three inquests so far held in these deaths returned open verdicts.
A verdict of suicide was returned by an inquest in the remaining case.
The Amnesty spokesman said: "Justice must be delivered to these families, but it must also be seen to be delivered.
"Closed door investigations of the army by the army will not suffice.
"Investigations must be thorough, independent and impartial and be seen to be so."
"The UK authorities must heed the call of many families of members of the Armed Forces for a wide-ranging public inquiry, in order to re-establish public confidence that justice and truth has been delivered."
Amnesty's support has been welcomed by Ms James's father, Des.
He said: "I think it's the secrecy that surrounds it all that gives it an air of conspiracy - and the increasing number of these undetermined deaths."