They included John Fowler, 57, a car dealer, charged with conspiracy to rob the Securitas depot at Tonbridge, Kent, and with kidnapping the depot's manager and his wife and young son.
The others were Stuart Royle, 47, charged with conspiracy to rob, and Kim Shackelton, 39, charged with handling stolen goods, a spokesman for Kent Police said.
On Wednesday police found the truck used by an armed gang to carry out what has turnred out to be the UK’s biggest cash robbery.
Dozens of police also searched a sprawling farm estate at Staplehurst in the county of Kent, in England's south-east, in the hunt for the gang.
The mob kidnapped the depot director, his wife and nine-year-old son at gunpoint in the dead of night.
Police believe the white Renault truck, a key piece in the jigsaw, was used to load the money at the depot. They also believed it was used to dump money crates in fields elsewhere in Kent.
At the Staplehurst farmhouse officers carried out a sweep across the grounds and police divers searched an ornamental well.
Kent police said they had been given permission by magistrates to keep questioning four people already held in custody.
Meanwhile police said another suspect, a woman, was arrested on Tuesday in relation the heist.
Raids were continuing across Kent and elsewhere in south-east
England as the police chase leads following a deluge of calls from the public.