Police officers at the security depot in Tonbridge, England. (Reuters)

Tonbridge (England), Feb. 23 (Reuters): Detectives hunted today for an armed and “callous” gang who posed as police to steal up to ?50 million in what could be Britain’s biggest-ever cash robbery.

Six raiders snatched the manager of a security depot in Tonbridge, Kent, 30 km southeast of London, took his wife and young son hostage and threatened to kill them unless he helped them get inside the compound, police said. “These men were armed, dangerous and violently threatening,” said detective Paul Gladstone.

Kent police said raiders in an unmarked car with police-style blue lights on its front grille, kidnapped the depot manager as he drove home from work on Tuesday.

He was taken to a farm building where a gun was placed to his head. He was told to cooperate or his family would be killed.

At the same time, his wife and son were abducted from their home by raiders dressed as police. Early today, the gang spent more than an hour loading a large white lorry with cash ? a mixture of new and old bank notes ? before escaping.

Airports and ports were put on full alert in case the gang attempted to flee the country and a ?2 million reward was offered.

The Bank of England, Britain’s central bank, confirmed that ?25 million of its money had been stolen. Assistant chief constable Adrian Leppard said the final figure could hit ?50 million.

If confirmed at ?50 million, it would eclipse the previous record theft of cash and valuables worth up to ?40 million from a safe deposit box centre in Knightsbridge, central London, in 1987. No one was injured in the raid on the depot .

The windowless depot, surrounded by a metal fence and cameras, stored banknotes used in shops across London and the southeast.

The depot is run by Sweden’s Securitas AB, the world’s biggest security firm.