It has emerged that a warning was given to a British Anglican priest serving in the Middle East by a purported al Qaeda chief months before the failed car bombings in London and Glasgow.

"Those who cure you are going to kill you" were the words in the cryptic warning given to Canon Andrew White in Jordan, a senior Anglican priest and vicar of St George's Anglican Church in Baghdad.

Canon White described how he met a man privately with a translator and sheik following talks with Sunni Muslim tribal and religious leaders on 18 April in Amman.

The Anglican priest was told by religious leaders that the man he was meeting was an al Qaeda leader who had travelled all the way from Syria to attend the meeting.

The Iraqi man, dressed in Western clothes, issued a warning of future attacks on Britain and the US, White said.

"It was like meeting the devil. He talked of destroying Britain and the United States and then said, 'Those who cure you are going to kill you.'"

Canon White is renowned in Christian circles as leading the Anglican Communion's only parish in Baghdad, and often acts as a bridge between conflicting political and militant leaders operating in the region. He is currently involved in numerous hostage negotiations in Iraq.

He admitted that he did not understand the significance of the al Qaeda leader's statement at the time.

Although he did report the threat to Britain's foreign office, he did not mention the comment, which could be interpreted as hinting at the involvement of doctors in a terror plot.

As recent events unfolded and it emerged that the suspects detained over the recent London and Glasgow attacks were workers in the NHS, the significance of the hidden message became apparent.

"As soon as I heard many of the suspects were doctors I remembered those words. I work with a lot of people who are not necessarily good people. It becomes very difficult to distinguish what threat is real and what is not," Canon White explained.

The eight suspects currently being held in the investigations over the London and Glasgow attacks include one doctor from Iraq and two from India. A physician from Lebanon, as well as a Jordanian doctor and his medical assistant wife are among the other suspects.

It is believed that another doctor and a medical student from the Middle East, possibly Saudi Arabia, were also part of the attack.

Several of the arrested men in the British plot were on a watch list compiled by the domestic intelligence agency MI5, a British Government security official said, indicating their identities had previously been logged by agents. The official did not say why they were put on the watch list.

It has also emerged that many of those held were on an MI5 watch list. A British security official said: "Some, but not all, have turned up in a check of the databases, but they are not linked to any previous incident."

Approximately 1,600 people are currently on the MI5 watch list, with details of hundreds more held by intelligence agencies.