The Guardian indicates that the recent bomb attacks in Britain were thwarted by means of surveillance of telephone and email traffic.

The plot to mount car bomb attacks in Britain was hatched outside the UK, with the doctors allegedly involved linked to a ringleader or mastermind abroad, counter-terrorism officials believe. One theory is that the alleged plot was orchestrated by one or two jihadists who infiltrated the NHS and indoctrinated others.

It emerged last night that investigators suspect that the two men caught at Glasgow airport trying to ram a Jeep into the terminal building were also behind the failed attempt to detonate two car bombs in central London last Friday.

Sources also suggested that all known members of the cell had been accounted for. “There is not a huge manhunt,” one well-placed official said. Though the terrorist threat level remains at “critical” there were indications that it would soon be downgraded to “severe”, meaning an attack is highly likely but not imminent.

All eight people arrested have links with the NHS – seven are doctors or medical students and one worked as a laboratory technician. All entered the UK legally.

Intelligence sources last night declined to say where the “guiding hand” or mastermind behind the plot was based. It is likely, given the dates on which some of the suspects entered Britain, that the plot was hatched a year ago, or even earlier.

Though MI5 insists none of the suspects arrested in connection with the plot were under surveillance, the mobile phones detectives recovered from the would-be car bombs contained details that matched material on the security service database. Counter-terrorism officials say data from the phones and email traffic was checked on the database used by MI5, MI6 and GCHQ, the government’s eavesdropping centre. Connections were found linking that information and communications abroad, which enabled the police and security services to speed up their investigations in Britain.

“This linkage allowed the police to move quickly,” said a source. The foreign intercepts included talk of jihad, an official added. Counter-terrorism officials say the links between members of the British-based cell were via the foreign intercepts. It is believed, for example, that Mohamed Haneef, the doctor arrested at Brisbane airport, had long conversations with one of the suspects arrested in Britain.