A former MI6 operative has issued a stark warning that Britain faces the threat of a catastrophic terrorist attack comparable to 9/11 or the 7/7 London.
Aimen Dean, who worked as a double agent within the terrorist organisation for eight years while feeding intelligence to British security services, believes an attack is inevitable.
"It's not about if another 9/11 or 7/7 attack will happen; it's about when," he told the Sun.
The former informant, whose undercover work proved instrumental in thwarting major plots against Western targets, warned the UK harbours "hundreds" of potential Al-Qaida sleeper agents who could be activated to strike at any moment.
Mr Dean argues Islamic extremism and Iranian influence represent the gravest dangers facing the West today.
His journey from terrorist to intelligence asset began in his teenage years, when he joined Al-Qaida and received bomb-making training in the Afghan mountains over an 11-month period.
During his time with the organisation, he worked alongside some of the world's most dangerous figures, including Abu Khabab, who oversaw the development of Al-Qaida's mass-casualty weapons programme until a CIA drone strike killed him in 2008.
His intelligence gathering for MI5 and MI6 proved invaluable in disrupting terrorist operations, most notably a planned attack on New York's underground transport network orchestrated by Khabab.
Aimen Dean said there could be hundreds of sleeper agents in the UK
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The information Mr Dean provided to British and American security services is believed to have prevented hundreds, possibly thousands, of deaths during his eight years operating covertly within Al-Qaida's ranks.
Mr Dean contends that Western governments have misdirected their attention by treating Russia as the principal adversary, when Tehran poses the more pressing danger to British citizens.
He argued Iran has provided sanctuary to Al-Qaida for a quarter of a century, creating conditions that have enabled sleeper cells to mount attacks against British nationals, including deadly assaults on UK citizens in the United Arab Emirates.
"A threat like Iran needs to be countered because of the fact that they are a nation that has sponsored terrorism," he stated.
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Aimen Dean warned an attack similar to the 9/11 atrocity could happen in the UK
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While acknowledging it remains "impossible" to determine the precise number of Al-Qaida operatives present in Britain, he insists the figure runs into the hundreds at minimum.
"Unfortunately, I would love to tell you the world is an amazing place, but it's not," he added.
Mr Dean's path to radicalisation began at just 17, when he encountered Khalid Sheikh Mohammed, the architect of the September 11 attacks, following a year spent fighting in Bosnia.
By 18, he had pledged his personal allegiance to Osama bin Laden and was receiving explosives training in Afghanistan, where his aptitude for mathematics drew him to the technical aspects of bomb construction.
However, the 1998 suicide bombings targeting American embassies in Kenya and Tanzania fundamentally altered his worldview.
The attacks claimed 200 lives and left 4,000 wounded, prompting Mr Dean to recognise he had chosen the wrong path.
To extricate himself from the organisation, he feigned illness and travelled to Qatar, where he formally renounced Al-Qaida.
Just nine days later, MI6 agents made contact, recognising his potential value as an intelligence asset.
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Mr Dean's covert operations brought him into contact with Al-Qaida's entire hierarchy, from bin Laden himself down to recruiters such as the notorious hook-handed preacher Abu Hamza at Finsbury Park Mosque.
His double life came to an abrupt end when Time magazine published an article online that, while not naming him directly, contained sufficient detail for Al-Qaida to identify their mole.
Mr Dean immediately contacted his MI5 and MI6 handlers and was rushed to London, where he was placed in protective accommodation and given a new identity.
He has since published a memoir detailing his experiences as an undercover operative.