Wardens at an English prison have foiled a daring escape plot by some of the country's most dangerous terrorists in a hijacked helicopter.

Al Qaeda henchmen on the outside planned to hire a chopper for "business," then force the pilot to land in the Full Sutton prison in East Yorkshire at gunpoint. Inside, the nine Muslim inmates were to kidnap the jail imam during prayers with weapons hidden in the prison mosque.

But jail bosses acting on a tip-off swooped on the plotters' cells hours before the escape bid was due to start.

The nine — including convicted terrorists — were imprisoned separately. They will now be transferred to other jails.

On Monday night, officials were hunting for weapons in the mosque, which doubles as a chapel.

One of the jailed terrorists is Omar Khyam, 27, who was sentenced to at least 20 years for his role in the 2007 plot to blow up Bluewater Shopping Centre in Kent and London’s Ministry of Sound nightclub.

Counter terrorism chiefs reportedly told the Justice Department that a helicopter was on standby for the audacious plot.

"This would have been one of the most damaging escapes ever," a source said.

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