"Its existence simply will not be sufficient to assuage grieving relatives, nor the public, that we were well served by our security services in this incident."
The committee, set up in 1994 with the task of overseeing the security services, has nine members hand-picked by the prime minister and reports to them.
The 500lb (227kg) Omagh bomb was planted by members of the Real IRA - renegade IRA members opposed to the Northern Ireland peace process.
Despite police inquiries on both sides of the Irish border over the last 10 years, at the cost of tens of millions of pounds, none of the bombers are in jail.
Well-placed sources told Panorama that GCHQ was monitoring the bombers' phones that day, a claim confirmed by Ray White, former assistant chief constable in charge of crime and Special Branch for the Northern Ireland police service.
Whether GCHQ could have helped stop the bombing comes down to whether they were listening to live exchanges between the bombers, allowing them to respond to events, or whether they were simply recording the conversations.
Mr White told Panorama that the Special Branch officer responsible for requesting GCHQ's assistance was "adamant" he had asked for live monitoring.
He said the officer did this "primarily for the purpose of triggering a pre-arranged surveillance plan" to interdict the bombers.
Some weeks before Omagh was attacked, the Special Branch was given a mobile phone number being used by bombers operating mainly from the Irish Republic. That number was passed to GCHQ for monitoring.
Special Branch officers say they asked GCHQ for live monitoring of the calls
Two weeks before the Omagh bomb, the town of Banbridge in County Down was devastated by a similar car bomb attack, in which 38 people were injured.
In the minutes running up to the Banbridge attack, GCHQ recorded a phone exchange between the bombers, including the phrase "the bricks are in the wall" - a code meaning that the car bomb had been parked and the device armed.
Phone billing records show the Omagh bomb run began in Castleblaney in the Irish Republic at around 12.40 on 15 August, with two mobiles having a 14-second exchange - the first of nine such exchanges both before and after the bombing.
One mobile was in the scout car which was checking the road ahead was clear, the other in the bomb car.
As Panorama reports, if intelligence officers were listening there were clues in the conversations, which though coded, could have acted as warnings.
At one point the scout mobile was called from a telephone box at a petrol station 100m (about 110 yards) inside Northern Ireland near Jonesborough.
Sir Ronnie Flanagan says he knew nothing of GCHQ's involvement
Special Branch, who were monitoring the phone box, identified the voice as that of Liam Campbell, a senior Real IRA commander suspected of involvement in previous bombings.
At around 1330, the words "we're crossing the line" were picked up from one of the mobiles, coinciding with one of the cars crossing the border into Northern Ireland at Aughnacloy.
By 1410 the cars were in Omagh, and at around 1420 came the same coded phrase used by the Banbridge bombers - "the bricks are in the wall".
At 1504 the bomb exploded, by which time the bombers were safely back in the Irish Republic.
After the bombing, Panorama says, Special Branch asked GCHQ what happened and was told: "We missed it."
Whether "missed it" was because GCHQ was simply recording the conversations, or whether officers had been listening in but had not understood the significance of the coded fragments, is not clear.
Last month saw the 10th anniversary of the attack
But, as Panorama reports, even if GCHQ could not have prevented the attack, more could have been done to help the investigation.
According to one of the sources who spoke to the programme, transcripts reporting exchanges with up to five mobiles associated with the bombers were sent to Belfast "within hours" of the bombing.
However, these were never disclosed to the detectives hunting the bombers.
In fact, Sir Ronnie Flanagan, former chief constable of both the Police Service of Northern Ireland and the Royal Ulster Constabulary (RUC), told Panorama he was unaware GCHQ had been monitoring the bombers' mobile phones.
Former RUC and PSNI Assistant Chief Constable Ray White said that sharing telephone numbers and the identities of those using the mobiles with the Criminal Investigation Department (CID) immediately "would have been, in a sense, manna from heaven".
He said that arrests could have been made in the "golden hours period" when forensic and other evidential opportunities were at their optimum.
Michael Gallagher, whose son was killed, wants a public inquiry
However, Mr White said Special Branch members have told him they did not receive details of GCHQ intercepts until three to four days after the bombing.
Special Branch insist that they gave this information, which had been sanitised by GCHQ, verbally to the CID 24 hours later.
Yet Panorama reports that while the Special Branch did brief the CID, police sources say there is no record in the CID log of a briefing until three and a half weeks after the bombing.
Even then detectives only received some of the names of the main suspects, with no details to help them build a case.
The fact that the bombers had used mobile phones, and that GCHQ had voice recordings and their telephone numbers, was withheld.
Consequently the CID was forced to spend nine months trawling through 6.4 million telephone records to finally identify 22 suspects' phones active in Omagh and four other bombings.
Although this proved which mobiles had been in Omagh, prosecutors needed evidence of who had been using them before going to court.
GCHQ had some voice recordings, but by law intercepts cannot be admitted as evidence. Panorama says there was nothing to stop the details from being shared with the CID to give them early leads.
In response to Panorama's findings, Michael Gallagher, chairman of the Omagh Support and Self Help Group, said: "We have been demanding a public inquiry since 2002 into the abysmal failure of the police inquiries.
"In all conscience the government can no longer resist this."
The government declined to respond to detailed written questions submitted by Panorama.
Panorama: Omagh - What the Police Were Never Told will be broadcast on BBC One at 8.30pm on Monday 15 September.
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