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A transport union has claimed there was a "serious lapse in security procedures" after it emerged the ringleader of the London Bridge terror attack was a former Tube worker.

TSSA suggested cuts to London Underground staff "compromised security and vetting procedures and let a self-proclaimed jihadi gain employment".

Khuram Shazad Butt worked as a trainee customer services assistant on the Tube network for six months last year despite having been the subject of a police and MI5 investigation in 2015 over his extremism. He left the role in October last year, confirmed Transport for London (TfL).

Manuel Cortes, general secretary of the transport and travel industry union, said: "The process of becoming employed on the Tube as a CSA should rightfully be a long one. Since 7/7 public transport is quite rightly a highly security-sensitised industry.

"It should take anywhere between four and six months from filling out your application form to your CSA induction day. There are two interviews, a variety of suitability tests and then security protocols are supposed to be applied.

"So this London Bridge killer will have applied for this position between October and December 2015 at the same time Boris [Johnson] was bludgeoning through nearly 1,000 job cuts on the Tube - which would downgrade safety procedure on the Tube and take out al 242 staff in the specialist CCTV monitoring unit."

Butt, 27, from Barking, appeared in a Channel 4 documentary about British Islamic extremists in January last year. The Jihadis Next Door showed him praying in front of a black Isis flag with other radicals in Regent's Park.

The British Pakistani killer, known among friends as "Abz", is alleged to have been an associate of the hate preacher Anjem Choudary was once thrown out of a mosque for interrupting an imam's sermon and verbally attacked an anti-extremism campaigner.

Former colleagues said he worked at Westminster and Canada Water stations while employed on the Underground.

Mr Cortes said: "My members on the Tube are furious that a self-proclaimed jihadi who praised terrorist attacks on his Facebook pages, and had been on TV inciting his racial and community hatred and it appears was an associate of the Tube's 7/7 attackers was left walking the streets let alone given a job on the Tube."

TSSA said Butt was not a member of the union.

A TfL spokesman said: “Khuram Butt worked for London Underground for just under six months as a trainee customer services assistant, leaving in October last year.”

It declined to comment further, citing the ongoing police investigation.