UK Home Office officials say one of those arrested is suspected not only of masterminding the foiled plot to bring down up to nine transatlantic airliners, but also of involvement in other planned atrocities over the past few years, the Times report said.

They believe he was instrumental in sending the ringleader of at least one previous British terror plot for training at a camp in Pakistan last year.

He is described by counter-terrorism officials at Britain's MI5 internal security service as the senior figure in a British terror network involving Kashmiri, North African and Iraqi cells, the Times said.

Scotland Yard, the headquarters of London's Metropolitan Police Service, believes the plot to bring down airliners involved up to 20 terrorists who were planning to smuggle liquid bomb components in hand luggage onto nine British and American passenger jets.

Their targets were planes leaving Heathrow and possibly three other British airports later this month.

The bombs were to be assembled on board by combining peroxide and acid-based substances into liquid explosives. The plan was to explode the devices simultaneously as the planes headed for cities in the United States.

Paul Stephenson, the deputy commissioner of London's Metro-politan Police, said it was a plot "to commit mass murder on an unimaginable scale". It is estimated that as many as 3,000 people could have been killed.

The thwarting of the alleged plot has, however, failed to quash continuing fears among UK counter-terrorism experts. Senior security officials have briefed ministers that a "second phase" of attacks may be about to be launched, the Times said.