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LONDON, England (CNN) -- Authorities in Kent, England, have appealed to the public for help in solving the armed robbery of a security company, which involved the kidnapping of a manager and resulted in the theft of 25 million pounds, or about $43.5 million.

The incident at the Securitas security depot in Tonbridge began Tuesday evening, according to a statement issued by Kent Police's serious and organized crime unit.

A depot manager was stopped by what he believed to be an unmarked police car about 6:30 p.m. Tuesday as he drove home from work, police said. The car was believed to be a Volvo with blue lights in its radiator grill.

"A passenger wearing a high-visibility jacket and police-style hat got out and spoke to the manager who, thinking these were genuine police officers, got back into the car with him where he was handcuffed," police said. The Volvo drove off. (Watch as police investigate the crime -- 2:04)

At about the same time, the manager's wife and young son were visited at their home by two men who said they were police officers and told them there had been an accident involving the manager. The wife and son were taken from their home, police said.

Meanwhile, the Volvo met up with a white van, and the manager was tied up, put into the van and driven to an unknown location, where he was threatened at gunpoint and told his family would be at risk if he did not cooperate, authorities said.

About 1 a.m. Wednesday, the manager was taken to the security depot. A white truck also arrived there, and six men -- at least some of whom were armed -- tied up the depot staff on duty "and then loaded a substantial amount of money" into the truck, police said.

"They left about 2:15 a.m. and staff raised the alarm about an hour later. No one was hurt during the incident, but the staff were all very shocked by what happened."

The statement did not address when the manager's wife and child were released, and did not divulge the amount stolen.

Police appealed to the public for information about the vehicles used, the statement said.

"In particular, officers would like to hear from anyone who saw the manager's silver Nissan car being stopped ... or who saw a Volvo or similar car rendezvous with a white van, or anyone who saw a white 7.5-ton truck in the Tonbridge area in the early hours of Wednesday morning."

"This was a traumatic ordeal for the manager of the security depot and his family and for all of the staff who worked there," Kent Detective Superintendent Paul Gladstone said in the statement.

"This was clearly a robbery that was planned in detail over time -- someone must have information that will help us in the hunt for the robbers. A very substantial sum of money running into millions of pounds has been stolen and we are determined to bring the robbers to justice."

According to its Web site, Securitas is a worldwide company that offers security services, security systems and direct and cash handling services for businesses.

The Wednesday robbery is one of the largest in United Kingdom history, but the largest all-cash robbery occurred in December 2004, when about $50 million was stolen from a bank in Belfast, Northern Ireland. That case remains unsolved.