The bulk of Islamism-related terror offences in the UK over the past decade involved British citizens with links to al Qaeda, according to a new report.
The Centre for Social Cohesion found that 69% of such incidents between 1999 and 2009 were carried out by home grown terrorists or would-be terrorists.
The research also suggested that seven of the UK's eight major bomb plot cells contained individuals with direct links to al Qaeda.
Only the failed London bombers of July 21, 2005, lacked undisputed evidence of direct contact with any proscribed organisation.
Some 48% of the 127 Islamism-related terror offences or suicide attacks were committed by individuals living in London, the report found.
The next two most common regions were the West Midlands (13%) and Yorkshire and the Humber (9%).
The report concluded: "Al Qaeda and al Qaeda-inspired terrorism remains the biggest threat to the UK's national security.
"The Security Service estimates that over 2,000 people in the UK pose a terrorist threat and in March 2005 it was estimated that there were up to 200 al Qaeda-trained operatives in the UK.
The report, Islamist Terrorism: The British Connections, stated that the British-based threat does not only affect the UK.
A number of British Muslims have been convicted in foreign courts or have fought for, or trained with, terrorist or extremist Islamist groups abroad, the report outlined.