Former MI6 spy claims new 9/11 attack could come at any time as 'hundreds' of sleeper agents living in UK

A former member of Al-Qaeda turned MI6 spy has shared a chilling warning about the amount of sleeper agents living among us in the UK.

Aimen Dean claims that there are probably 'hundreds' of undercover operatives blending in amongst Brits who are willing to unleash terror at any moment.

Worryingly, he reckons that a terror attack which could be on par with the devastation inflicted on 9/11 is on the horizon, as he warned that it's 'not about if' it will happen - 'it's about when'.

And given his background, he has more of an understanding of how things work.

The Saudi Arabia-born spy spent eight years gathering intelligence for Britain's security and intelligence services - MI5 and MI6 - after rising through the ranks in Al-Qaeda.

The self-described 'bookish nerd' became an integral part of the militant organisation, seeing him build bombs and train up new recruits, until he had a drastic change of heart in 1998.

He explained that 'the horror' of what he was doing only started to 'sink in' when he saw the devastation that the nearly simultaneous bombings of US embassies in Nairobi, Kenya and Tanzania were carried out.

Aimen Dean reckons a terror attack comparable to 9/11 could rock the UK (Spencer Platt/Getty Images)

The attacks left 200 people dead, while another 4,000 were killed - and Dean soon became disillusioned by the group he had pledged allegiance to.

"That's when I started to have doubts about the legality of the whole thing," he previously told the BBC, explaining that he started to question the 'religious justifications' of Al-Qaeda's attacks.

"Two months down the line, I decided that it's no longer for me and that I wanted to leave."

Dean - who was previously affiliated with terrorist figures such as Osama Bin Laden, Khalid Sheikh Mohamed, Abu Zubeida - feigned illness and travelled to Qatar with the intention of abandoning his affiliation to Al-Qaeda.

Nine days after he arrived, he explained that he 'landed in the lap' of MI5 - who managed to convince him to become a spy.

He did so for the next 8 years, seeing him travel back and forth between Afghanistan and London, while gaining crucial intelligence for Britain's security services.

The former agent, who's special skills include a photographic memory and a flair for map reading, is thought to have saved thousands of lives thanks to his work.

Notably, Dean helped foil a plot to bomb the New York Subway, while he also claims to have thwarted suicide bombings and the use of poisons on innocent civilians, according to the BBC.

The former MI6 spy believes that there are 'hundreds' of sleeper agents currently in the UK (CNN)

Now the former agent, who's cover was blown back in 2006, has shared a worrying assessment of the current terror threat in the UK.

Dean believes that there could be 'hundreds' of Al-Qaeda sleeper agents in the country, who are ready to unleash devastation whenever they are called upon.

Speaking to The Sun, the father-of-one warned: "It’s not about if another 9/11 or 7/7 attack will happen; it’s about when.

"The biggest threat to the UK and Europe right now isn’t Russia, but the spread of Iranian influence. We’re going to see many more lone-wolves acting for the regime.

"When it comes to sleeper agents in the UK, it’s impossible to tell how many there are...but there are hundreds.

"Islamic fundamentalism is much more sinister as it undermines from within. It pushes people to distrust institutions and in some ways is much more dangerous than violent extremism.The violence is just the tip of the iceberg."

Sharing his bleak outlook on what the current tensions across the globe could signify, Dean continued: "Unfortunately, I would love to tell you the world is an amazing place, but it’s not.

Osama Bin Laden previously led Al-Qaeda before his death in 2011 (CNN via Getty Images)

"The problem is the new world order is now the new world nightmare. We have rogue nations such as Iran aspiring to become nuclear powers.

"And a threat like Iran needs to be countered because of the fact that they are a nation that has sponsored terrorism."

According to the UK government, the current threat level of another terrorist attack is 'substantial' - meaning that 'an attack is likely'.

MI5 also states that 'Islamist terrorism is the most significant terrorist threat to the UK by volume'. MI5 also noted 'extreme right-wing terrorism, Northern Ireland-related terrorism and, to a lesser degree in terms of volume, left-wing, anarchist or single-issue terrorism.'

Sharing an update on the current threat last month, the director-general of the Security Service Sir Ken McCallum said: "Groups overseas are continuing their attempts to direct terrorism into the UK and Europe.

"Al-Qaeda and Islamic State are once again becoming more ambitious, taking advantage of instability overseas to gain firmer footholds.

"They are both personally encouraging and indirectly inciting would-be attackers in the West."

Dean said that the UK needs to take action to 'counter' the current alleged threat to the safety of British nationals.