Britain's biggest terrorism trial has just ended with the conviction of men who conspired to build a massive homemade bomb. But with the lifting of reporting restrictions, Panorama reveals the truth about what MI5 really knew about the July 2005 London bombers.
Why weren't the leads followed up?
The public has never been told the full story about the links between the fertiliser bomb plot, known as Operation Crevice, and two of the 7 July suicide bombers.
But was there an opportunity to identify them in advance? Did the security services make a serious mistake and was an opportunity missed? Panorama believes the evidence clearly indicates there was - but that it does not necessarily mean that the attacks could have been prevented.
The missed opportunity happened during an MI5 surveillance operation on 2 and 3 February 2004 - 17 months before the London bombings. The officers were watching Omar Khyam, the ringleader of the fertiliser bomb plot.
They had been watching Khyam for almost a year after he had first appeared on their radar in Luton as part of an investigation into suspected Al Qaeda connections in the UK.
2 FEB 2004: FIRST SURVEILLANCE
1: MI5 team watching Omar Khyam in Crawley spot him in a car with Khan and Shehzad Tanweer.
2: MI5 tails Khan and Tanweer after they leave Crawley. Officers photograph Khan at M1 Toddington Services, Bedfordshire.
3: Khan reaches West Yorkshire. Car seen parking outside family home in Dewsbury. Checks reveal car registered to Khan's wife. No further action taken.
By February 2004, they had stepped up their surveillance - but Scotland Yard's Anti-Terrorist Branch were not yet involved as at the time it was a purely MI5 intelligence gathering operation.
On 2 February, MI5 officers noted two strangers talking to Khyam. They would later turn out to be Mohammed Sidique Khan and Shehzad Tanweer - two of the London suicide bombers.
I have seen MI5's surveillance log - and what it records happened next. The details were never revealed in court because of reporting restrictions. According to the log, a Honda car, registration R480 CCA, was seen in Langley Parade, Crawley. Omar was in the passenger seat and the driver was Khan.
MI5 ran a check on ownership of the vehicle. The name meant nothing at the time. It was registered in the name of Khan's wife.
Although they did not know who he was, the officers followed the car after it left Crawley, not knowing where it was going. After Khyam was dropped off, Khan drove onto the M1 and headed north.
When it stopped for petrol at Toddington services, MI5's log states that photographs were taken of the passengers. MSK was covertly snapped in the vicinity of Burger King at the entrance to the services' refreshment area.
Was the photograph clear enough to identify him? The intelligence services say the quality was very poor. But other sources who have seen it told me that Khan was identifiable. Panorama asked to see the photograph, but the request was refused. We understand that one other photograph, said to be of marginally inferior quality, was subsequently taken of MSK going into an undisclosed internet café.
Followed to Leeds
According to MI5's log, officers followed the Honda for a further 150 miles to Leeds. It notes the addresses and locations where some of the passengers got out.
The Honda, with Khan at the wheel, was eventually seen parking out side his family home in Dewsbury. The log notes the precise address.
Car: MI5 officers followed it to Leeds (reconstruction)
Within weeks, the investigation into Khyam had become a major operation, leading to arrests in Canada, the UK and Pakistan.
In June 2004, the intelligence services again checked out the car. This time, they found it had been re-registered in the name of 'Siddeque Khan'. Again, at the time, the name meant nothing.
In their investigation into the background to the 7 July London bombings, Parliament's Intelligence and Security Committee (ISC) gave MI5 a clean bill of health.
It confirmed that Khan and Tanweer had appeared on the radar of an earlier investigation - meaning Operation Crevice. But it concluded: "the decisions not to give greater investigative priority to these two individuals were understandable".
But the ISC was either never given the full details of the 2 February surveillance operation or was informed but chose to omit key facts - details which might have fuelled demands for the public or independent inquiry the government has resisted.
While the ISC's report was crafted to avoid prejudicing the Crevice trial, it could have alluded to the 2 February surveillance operation without linking it to Omar Khyam.
MI5's position is that neither Khan nor Tanweer were under Security Service or police surveillance.
But Conservative shadow Home Secretary David Davis had a different view - and has called for a full independent inquiry.
"That clearly is not true," he told Panorama. "It's self evidently a surveillance operation. They're being followed, they're keeping somebody under observation, they're making a note of where they're going, they're presumably making a note of the car itself, and the times, and who's there.
"All those things amount to a surveillance operation. They let somebody to go off surveillance who subsequently turned out to be a suicide bomber."
The Old Bailey heard that Khan and Tanweer were spotted with Khyam on three more occasions - although both the police and MI5 say they were still not identified by name.
But the serious mistake that Panorama has identified is that at the time MI5 never informed West Yorkshire Special Branch about the surveillance operation that ended up in its patch.
OTHER 2004 SURVEILLANCE OF MSK
1: 21 February: Khan logged getting into Omar Khyam's bugged car; Khan recorded asking Khyam if he is "a terrorist". Khan joins group discussion at house in Crawley, attended by the alleged detonator designer.
2: 28 February: Khan joins Khyam at 0900 for trip from Crawley to Wellingborough, Northants. Tanweer also in the car. At destination, they use internet café and then drive to Slough by 2300.
3: 23 March: Khan and Tanweer go to Khyam's Slough flat. Bugged conversation on light-hearted themes, but also discussions of fraud.
It never told them about the Honda, its registration number, the name of its owner, the addresses and places where the passengers had got out or its final destination.
Nor did it show them the photograph of the 'stranger' covertly taken at Toddington services.
It never asked local West Yorkshire Police Special Branch officers if they knew anything about the individuals or the addresses and, if they didn't, to try and find out, given concerns about the cell they had been seen associating with.
There is however a tantalising hint of what the ISC knew amongst the conclusions to its report.
"The Security Service and Special Branches [need to] come together in a combined and coherent way to tackle the home grown threat," said its report. "We are concerned that more was not done sooner."
The lesson was clearly learned. Today there are new Counter Terrorism Units manned jointly by MI5 and local anti-terrorist and Special Branch officers located in West Yorkshire, Manchester and Birmingham. Luton is expected to have one soon.
So why weren't the leads followed up?
Operation Crevice led to investigations into 55 suspects, with only 15 of them thought to be directly connected to the bomb plot. Khan was not one of these. One bugged conversation focused on fraudulent fund raising, possibly for Al Qaeda's coffers - but there was no indication Khan himself was planning to bomb the UK. The Security Service was looking at up to 50 terrorist networks in the UK.
The most pressing and potentially deadly plot, also uncovered in 2004 amid massive pressures on resources, led to the jailing of Dhiren Barot for 40 years last November for plotting mayhem in the UK.
Deputy Assistant Commissioner Peter Clarke, National Coordinator for Terrorist Investigations, told Panorama about the logistical challenge of running surveillance - explaining how resources are the crucial factor.
"An average surveillance team is perhaps 15 to 20 people strong," he said. "In order to keep one person under 24 hour surveillance you'll need a minimum two, perhaps three, surveillance teams for each person. Three surveillance teams could be anything up to 60 people."
Today, as the Crevice plotters face prison, it's believed there are over 200 networks still under investigation.
A genuine threat?
However, the agencies say there was another reason why Khan was not a priority target.
When he was subsequently spotted three times in the company of Omar, the bugged conversations indicated they were not talking about attacking the UK but about ripping off banks, companies and financial institutions.
According to Peter Clarke, the money was destined for Al Qaeda's coffers and the conversations indicated that Khan was planning to leave for Pakistan and possibly to fight in Afghanistan.
Indeed, in one conversation Khan, who was expecting to become a father, was worried about saying goodbye to his baby.
Could 7/7 have been stopped? Had MI5 brought West Yorkshire Special Branch into their confidence at the time, MSK could have been identified, watched, followed and fed into the wider intelligence picture over the following seventeen months before he launched the fatal attacks.
West Yorkshire police say the first they knew that MSK was the leader of the London bombers was after 52 people had died.
Dr John Reid told the House of Commons this afternoon that the Intelligence and Security Committee was satisfied that there had been no wrongful conduct regarding West Yorkshire Police.
Panorama stands by what it has been told by senior intelligence sources in the force - that at the time they knew nothing of MI5 following Khan and Tanweer to Leeds and Dewsbury on 2-3 February 2004.
Panorama reporter: Peter Taylor
Producer: Howard Bradburn
Editor: Sandy Smith