Authorities blamed criminal gangs — not terrorists — for the heist, and said the hunt continued for other robbers. 

"This is organized crime at its top level. This was planned and executed with military precision," Assistant Chief Constable Adrian Leppard said of Wednesday's pre-dawn raid in the market town of Tonbridge, 30 miles southeast of London. No one was injured in the robbery. 

The two suspects were arrested at two addresses in southeast London; police and forensic teams searched both locations. 

"All I can say is that the arrests are significant," Leppard reporters on the steps of the Kent police headquarters. He said police have received more than 400 calls from people offering tips, but would not provide any more details on the investigation. 

The heist at Securitas Cash Management Ltd. began when some of the thieves, dressed as police officers, stopped the firm's manager about 20 miles from the cash depot as he drove home Tuesday night. The manager got into their car, which he believed to be a police vehicle, and was handcuffed, police said. 

At the same time, a second team of masked thieves went to the manager's house in the town of Herne Bay and persuaded his wife and his 8-year-old son to go with them by saying the man had had an accident. The manager allegedly was told to cooperate or his family would be hurt. 

At around 1 a.m. Wednesday, several hours after the manager was seized, the group holding him went to the cash depot. They tied up the manager and 14 other employees and then took about an hour to load the cash into a truck, police said. About an hour after they left, the staff managed to call police. 

The Tonbridge raid bore similarities to the 2004 Northern Bank robbery that netted thieves $46.1 million. 

In both cases, thieves targeted a bank's cash distribution center — and used hostages to breach security. During both heists, police say, the raiders disguised themselves as police to gain the confidence of their victims. 

"I would doubt very much whoever did it had a terror link," Magnus Ranstorp, a terrorism expert at the Swedish National Defense College, said of Wednesday's robbery. "Normally, they don't go for high-risk ventures with massive amounts of law enforcement focus." 

Three men, including a bank employee, have been arrested and charged in the 2004 robbery. International authorities have blamed the outlawed Irish Republican Army, but British police suspect an organized crime gang. 

The Tonbridge robbery unfolded like the plot of the new movie "Firewall" starring Harrison Ford as a bank's security-software expert whose family is taken captive and threatened with death. 

Police offered a $3.5 million reward for information leading to the recovery of the Tonbridge cash — a stack that could weigh 900 pounds. 

Authorities issued an all-ports alert but said they were trying to come up with descriptions of the robbers. Some wore balaclavas and goggles. 

Video footage was released of a white van the robbers used to carry the cash. Several other vehicles used in the robbery were still missing. 

Bank officials have not yet determined the exact amount that was stolen, but said the notes included marked and unmarked bills. 

The robbers will have a difficult time laundering or converting such a large amount of cash, said British expert Peter Lilley. 

One option would be to take the cash to a country with looser monetary regulations where it could be put in offshore accounts or invested, he said. "Physical money possesses greater risk than electronic money or even gold," Lilley said. 

The depot, a single-floored, windowless building, is near the center of Tonbridge. It is surrounded by six-foot high steel fencing, and security cameras cover every entrance. Steel traps are in place to prevent unwanted vehicles from entering the compound. There are no signs to indicate the building stores large amounts of money.