Some of the suspects arrested in connection with the terror plots in London and Glasgow were known to MI5 before the attacks took place, it has emerged.
A number of those detained had appeared on the MI5 database.
Whitehall sources said that the Security Service had established “linkages” with a number of the individuals although it was not clear how much was known about them.
Nevertheless the sources said that MI5 had been able to pass on valuable information to the police which had helped to speed up their operation.
“It has taken a while but it appears that there are some linkages which refer to some of the individuals that have been detained,” one source said.
“As a result of these linkages we have been able to assist the police in their investigations and to help speed up some of the investigations.”
The sources stressed that they had always expected that traces of at least some of the suspects would crop up somewhere in MI5’s computer files.
They said that it would have been a matter of concern if there had been no references to them as it would have meant that they were not doing enough or that they were looking in the wrong areas.
While it was not clear whether all the members of the network had been captured there was a sense that the police believed that they had the main players.
According to reports, the men involved in car bomb attempts in central London were also involved in the attack in Scotland on Saturday, when a Jeep Cherokee was driven into the arrivals hall at Glasgow airport.
The Joint Terrorism Analysis Centre will decide in the coming days whether there should be any lowering of the threat level – currently assessed as “critical”, the most severe rating suggesting an attack is imminent.
All eight people arrested in connection with the attacks have links to the NHS.
Seven are believed to be doctors or trainee doctors while the one woman under arrest is a trained laboratory researcher.
A man arrested at Brisbane Airport on Monday was identified as Dr Mohammed Haneef, 27, who once worked at hospitals in Cheshire.
Details of the link between the arrested men and women and the medical profession have sent shockwaves through the health industry.
Dr Hamish Meldrum, of the British Medical Association, said: “Like others we were shocked to hear of the recent attempted bombings.
“The news that members of a caring profession may be involved in these atrocities was even more appalling.”
As the fast-moving investigation continued, the three terror suspects arrested in Scotland, Dr Bilal Abdulla and two trainee doctors, were transferred to Paddington Green police station in London.
It also emerged that Dr Abdulla visited Glasgow Airport at least once by taxi before it was attacked by a burning Jeep on Saturday.
Two men were arrested under terror laws at a Blackburn industrial estate yesterday as police reportedly investigated the sale of gas canisters. Police sources said no link had yet been found with the London-Glasgow investigation.
Searches are being carried out at an industrial unit on Birley Street, where the arrests were made and a Volvo S40 vehicle that may be connected with the investigation has also been removed for examination.
Police are investigating a possible sighting of the Jeep used in the airport attack at West Skelston Services in Heathhall, Dumfries, days before the attack.
Dr Haneef, who is working as a registrar at the Gold Coast Hospital, was detained while trying to board a plane to India with a one-way ticket.
He is one of two doctors held by police as part of the terror probe linked to the Halton Hospital in Runcorn.
The second doctor is a 26-year-old man arrested in the Lime Street area of Liverpool on Saturday.
Doctors from the Royal Alexandra Hospital in Paisley, Scotland, and the University Hospital of North Staffordshire in Stoke-on-Trent have also been arrested.
Two trainee doctors were arrested at the Royal Alexandra Hospital where a number of searches and controlled explosions have been carried out.
Dr Mohammed Asha, 26, who was arrested with his wife, Marwa Asha, 26, a laboratory researcher, on the M6 motorway, worked at the Stoke-on-Trent hospital.
One man critically injured in the car bomb attack on Glasgow Airport is being treated at the Royal Alexandra Hospital.
The Muslim Council of Britain issued a condemnation of the “barbarity” of the attacks.
Secretary-general Dr Muhammad Abdul Bari said: “Let us be absolutely clear about this, that those who seek to deliberately kill or maim innocent people are the enemies of all of us.”
Meanwhile, travellers using Heathrow Airport’s Terminal 4 faced major delays yesterday after a suspect bag sparked an alert.
The departure lounge was evacuated so passengers could be security checked for a second time.
All European departures were cancelled.
Controlled explosions have been carried out on a car at a Glasgow mosque and at a Tube station in Hammersmith, west London.
A warning was sent to Canon Andrew White, a British cleric working in Baghdad last week from an alleged al Qaida leader in Iraq.
An alleged al-Qaida leader in Iraq warned that his group was planning an attack and that “those who cure you will kill you”.
The Britidsh Foreign Office said that the official who Canon White had spoken to about the warning “did not remember the conversation”.
Mosques and Islamic organisations in Glasgow will hold a rally on Saturday to demonstrate their resolve against terrorism.
Faith leaders, churches, trade unionists and others in civic society are expcted to attend, while British Deputy First Minister Nicola Sturgeon has been confirmed as a speaker.