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Four of the men were on day release from HMP Standford Hill, an open prison on the Isle of Sheppey in Kent.
They are understood to have been working in jobs on temporary licence and staying in the jail overnight.
Three of the men have been charged, with the other seven released under investigation.
Four of the men were on day release from HMP Standford Hill (pictured) - an open prison on the Isle of Sheppey in Kent
Detective Chief Inspector Mark Brookes said: This seizure has stopped dangerous drugs from reaching the streets of London and beyond, where they have the potential to cause great harm to people and communities.
Ten held as drugs worth £10m seized at north London warehouse Anthony France
Ten men have been arrested after more than £10 million of drugs were seized at an industrial unit in north London.
Detectives spent months investigating the gang made up of six Turkish suspects, three Britons and one Italian national.
Officers raided the warehouse in Enfield and discovered 109kg of cocaine and 15kg of heroin with a street value of £10,220,000 on Tuesday.
The suspects aged in their 20s, 30s and 40s are currently being questioned in police custody.
The National Crime Agency and Metropolitan Police had launched a joint probe.