A senior police officer said on Thursday: "It's at least 20 million pounds ($35 million). It could be as high as 40 million, or even 50 million".
Adrian Leppard, the assistant chief constable of Kent police, however, revealed that the exact amount taken from the Securitas main cash depot in Tonbridge, southeast England, in Tuesday's raid would not be known until extensive forensic work was complete.
The raid, probably the result of months of extensive reconnaissance work, according to Leppard, saw the depot manager and his wife and eight-year-old son abducted separately and 15 workers held at gunpoint.
They were later identified by Britain's domestic Press Association news agency as Colin Dixon, 51, his wife Lynn, 45, and their son, Craig.
The kidnappers, who forced Dixon to help them gain access to the cash, were disguised as police officers while the others, possibly up to six, were said to be masked and wearing boiler suits.
Leppard said it was "an obvious line of inquiry" that the raid was conceived and carried out with inside knowledge and he was keeping an open mind into what happened. The money was a mixture of used and new banknotes.
He also could not say whether the gang might have fled via the Channel Tunnel, 80km away.
Thursday's Daily Mail newspaper said CCTV footage was being checked to determine if they escaped to France.
Leppard told reporters in Maidstone, Kent, that more than 100 police officers were currently hunting the raiders and that an unprecedented two million pound reward was being offered for information as to their whereabouts or identities.
All British ports and airports have been put on alert for anyone attempting to leave the country with large sums of cash while CCTV images of the gang's white delivery lorry was released to help track down those responsible.
A detailed forensic investigation
is now under way
"We know this for a fact - this is organised crime at its top level. It was planned and executed with military precision," Leppard said.
He said Kent police had the manpower, resources and wherewithal to pursue the robbers, vowing: "There's no doubt in my mind that we will catch these people and convict them."
Leppard said they were in touch with police in Belfast, Northern Ireland, where £26.5 million was stolen in a raid at the headquarters of the Northern Banks, making it the biggest cash theft in British or Irish history.
Foreign police, Scotland Yard, plus Britain's National Crime Squad and National Criminal Intelligence Service, which deal with serious and organised crime, have also been informed.
Police said that depot staff raised the alarm about an hour after the gang had left. They added that none of the staff was injured and they were being interviewed.
"We know this for a fact -- this is organised crime at its top level. It was planned and executed with military precision"
assistant chief constable,
Paul Gladstone, detective chief superintendent from Kent police, said earlier on Thursday that the robbers were "armed, dangerous and violently threatening" to kill Dixon and his family.
"We can be thankful that everyone was found unharmed," he added.
Paul Kenny, the acting general secretary of Britain's GMB union, repeated calls for extra measures against attacks on security vehicles carrying cash.
There were 836 attacks in 2005, up from 763 in 2004 and 697 in 2003, with security guards being shot, attacked with iron bars, machetes, stabbed, pistol-whipped and beaten up, according to union figures.