According to the Telegraph, al-Awlaki was invited to speak to a number of groups across the country despite being a suspect in the September 11 attacks.
Security sources are concerned that Awlaki's teachings became so widely acceptable that there are a number of Muslim disciples prepared to follow his advice and launch attacks in Britain.
Awlaki reportedly lectured for the Muslim Association of Britain, the Federation of Student Islamic Societies (FOSIS), and the Islamic Forum Europe (IFE) based at East London Mosque.
He began a "grand tour" of Britain from London to Aberdeen as part of a campaign by the Muslim Association of Britain, in which one lecture was held in conjunction with the London School of Economics, Imperial College, King's College and the School of Oriental and African Studies, all part of the University of London, the paper said.
Al-Awlaki was also a keynote speaker at the "ExpoIslamia" event held by the Islamic Forum Europe and appeared at an event at East London Mosque called "Stop Police Terror" in which he told his audience: "A Muslim is a brother of a Muslim, he does not oppress him, he does not betray him and he does not hand him over... You don't hand over a Muslim to the enemies."
During his stay in Britain, Awlaki was also reportedly working on 'Constants in the Path of Jihad', which he produced in 2005, a few months after being banned from the country.
Roshonara Choudhry, who was jailed for 15 years this week after trying to stab the MP Stephen Timms to death for his support of the Iraq war, had earlier admitted Awlaki's preaching on YouTube influenced her to take such a step.
The paper quoted Alexander Meleagrou-Hitchens, an expert on Awlaki at the Centre for the Study of Radicalisation at King's College in London, as saying: "It would be no exaggeration to say that his reception was unprecedented - to this day almost no other foreign-based preacher has compared."
He also said: "the official line, from many prominent individuals and organisations, was that Awlaki's radicalisation had been an insidious process that had caught them unawares," and added his views on violent jihad "would have been obvious to any regular consumer of his output." (ANI)