LONDON (Reuters) - Investigators are tracing their way through a maze of foreign links to a failed bomb plot in Britain to establish the possible role of al Qaeda's inner circle or its Iraqi arm, security sources said on Thursday.
Police and intelligence agencies were still trying to determine how eight people arrested in a suspected militant Islamist plot to bomb London and Scotland had come into contact with each other.
Two are from India, six from the Middle East and all had medical connections, including at least four doctors. None has so far been charged in connection with two unexploded London car bombs and a botched attack on Glasgow airport in Scotland using a fuel-laden jeep, which burst into flames.
"All the overseas angles are being followed up," a security source said. "The significance of overseas associations is very high up on our list of questions that we want answers to."
Police would not confirm a CNN report that they had found a suicide note in the wreckage of the jeep. While Prime Minister Gordon Brown has spoken of al Qaeda links to the attempted bombings, the extent of these remains unclear.
Security analysts say it is rare for cells to arise spontaneously without a guiding hand from professional militants. On the other hand, they are puzzled by the slapdash nature of the latest plot, which triggered a top security alert but claimed no victims and left behind a series of clues.
The British tabloid newspaper the Mirror reported that four of the suspects met in the university town of Cambridge in 2005, suggesting the group might have been formed then.
A security source said investigators still had an open mind on the question of whether the suspects met, and become radicalized, before or after they arrived in Britain. The families of two of them -- an Indian and a Jordanian -- have denied they were militants and voiced disbelief at the arrests.
Britain has seen a marked increase in al Qaeda-type plots since it joined the United States in invading Iraq in 2003.
An intelligence paper leaked to the Sunday Times in April said the country faced threats not only from "core" al Qaeda, based in Pakistan and Afghanistan, but also increasingly from al Qaeda in Iraq (AQ-I).
It said AQ-I networks were "active in the U.K." and there was intelligence that AQ-I's Kurdish network in Iran might be planning a large-scale attack on a Western target.
Officials said they were closely liaising with foreign intelligence services in the latest case.
Several plots in Britain have been directed or inspired by al Qaeda figures abroad. Two of the four British suicide bombers who killed 52 people in London in 2005 were believed to have associated with members of the network in Pakistan.
Dhiren Barot, convicted last November of planning several attacks including one to blow up cars packed with gas canisters, had traveled to Pakistan to present the scheme to his "al Qaeda overlords", his trial judge said. Gas cylinders were found in all three vehicles involved in the London and Glasgow incidents.
In another British bomb trial, evidence emerged of contacts in Pakistan in 2003 between one of the plotters and a senior Iraqi al Qaeda leader, Abd al-Hadi, now held at the U.S. military prison in Guantanamo Bay, Cuba.
The memo leaked to the Sunday Times said Hadi had urged a "large-scale" attack on Britain, ideally before Prime Minister Tony Blair stepped down. The London car bombs were found two days after he handed the premiership to Brown and were followed a day later by the airport attack in Brown's native Scotland.
Several other clues point to the possibility that foreign militant circles knew in advance of the latest plot to bomb Britain, and even that it might involve doctors, although authorities are cautious about their significance.
A British Anglican cleric in Baghdad has said he received a veiled warning from an al Qaeda figure in Jordan three months ago that attacks were planned against Britain and the United States and "the people who cure you will kill you". A Foreign Office spokesman said his account was passed on to the police.
A message on an Internet forum linked to al Qaeda, posted just hours before the London car bombs were found, said: "Today I say: rejoice, by Allah. London shall be bombed." However, a counter-terrorism official said such "aspirational" statements were common, and the timing might be a coincidence.