The move comes after campaigners said new evidence pointed to a possible failure of software in the onboard computer.

The information comes from an internal MoD document written by aircraft-testing experts nine months before the tragedy. It said the Chinook’s software was “positively dangerous” and that deficiencies meant the pilots’ full control of the engines “could not be assured”.

The document, written by a senior engineering officer at the MoD’s air testing centre at Boscombe Down, Wiltshire, said the hazard analysis of the Mark 2 Chinook showed its computer software was “safety critical” and that any malfunctions could have “catastrophic effects”.

Controversially, RAF top brass overturned an initial verdict and found Flight Lieutenants Jonathan Tapper, 30, and Rick Cook, 28, guilty of gross negligence after Chinook ZD576, travelling from RAF Aldergrove near Belfast to Fort George near Inverness in June 1994, crashed in thick fog on the Mull of Kintyre.

All 29 people on board perished, including senior members of Northern Ireland’s military and intelligence community. At the time, their deaths were described as a “catastrophic loss in the fight against terrorism”.

Campaigners and relatives of those killed have insisted flaws in the helicopter were likely to have caused the crash, not pilot negligence. They believe the aircraft was rushed into service without proper checks and the pilots were blamed to save the MoD’s face.

Three inquiries, including one by MPs, have found the cause of the crash inconclusive and said that, consequently, the pilots should not be blamed. But an official RAF board of inquiry concluded the helicopter was airworthy and blamed Flt Lts Tapper and Cook.

Sir Malcolm Rifkind, Defence Secretary at the time, said he had been unaware of the warnings about the Chinook’s computer software. The RAF, which knew of the problem, maintained it could not have caused the crash and therefore did not draw it to the attention of ministers, he said.

The Conservative MP insisted this was a “serious mistake” and that the verdict against the pilots was now “unsustainable”.

Sir Menzies Campbell, the former Liberal Democrat leader, said the new information confirmed his view that “an injustice has been done” and called for the board of inquiry to be reopened.

Angus Robertson, the SNP leader at Westminster, said the MoD’s position was “untenable”. The pilots had been made scapegoats and “must be exonerated”.

David Davis, the former shadow home secretary, who chaired a Commons inquiry into the disaster, said: “I would ask the MoD to quash the finding of gross negligence, which smears the reputation and honour of two brave, young and very capable pilots.”

The Yorkshire MP added it was “now long past time that the RAF recognised reality and removed this unnecessary and unjust stain on their characters”.

However, the MoD insisted that nothing had been brought to light which justified reopening the official inquiry. It said the latest information “could not be classed” as new evidence because it was in a document available to the inquiry team.

Mike Tapper, the father of Flt Lt Tapper, said: “I don’t think we’ll get anywhere under this government, who really lack any sort of leadership to sort this out.”