Hugh Doyle, a plumber who lives in Enfield, was arrested on Tuesday in a series of raids by around 200 police officers.
Two men arrested in Dartford were earlier named as Brian Reader and his son, also named Brian, but known more widely as Paul.
Customers leaving reviews of Mr Doyle's plumbing business described him as "a perfect gentleman" and "very professional [and] punctual".
"Hugh and his boys were definitely my Knights in shining Armour," another wrote, referring to Mr Doyle's plumbing team.
More than 12 properties were hit by police yesterday. Four suspects - aged 67, 74, 58, and 48 were arrested in Enfield.
A 59-year-old man was detained in east London, while a man aged 76 was held in Dartford, with a 50-year-old.
All those detained were arrested on suspicion of conspiracy to steal.
Hatton Garden jewellery heist
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Between 60 and 70 safety deposit boxes were opened by thieves during the 7 April raid on Hatton Garden Safe Deposit Ltd, the Metropolitan Police has said.
The eponymous street is well known for its Jewellery shops.
There was no sign of forced entry in the raid; thieves had disabled a lift an on the second floor of the building and climbed down a shaft to the basement, where they used a drill to bore holds into the subterranean concrete vault.
An official figure of losses has not been declared in full but estimates have placed the haul at around £200m.
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