Police have arrested two people over the record £50m robbery of a security depot on Wednesday but officers believe some or all of the armed gang may have escaped to the Continent.
A £2m reward is being offered for the recovery of the banknotes and capture of the raiders, who were described as a team of "top-level" criminals.
Detectives are also investigating the possibility that the IRA gang behind the £26m robbery at the Northern Bank in Belfast in 2004 were responsible for the raid on the Securitas depot in Tonbridge, Kent.
Police believe the robbers almost certainly had "inside" help and staff - serving and former - are being investigated.
Last night, a man aged 29 and a woman aged 31 were arrested in the Forest Hill area of south London. They were being held at undisclosed police stations in Kenton suspicion of conspiracy to commit robbery.
Adrian Leppard, Assistant Chief Constable of Kent Police, said the two arrests were "significant and directly related to the investigation". He said the two people were arrested at separate addresses in Forest Hill, which were both being "extensively searched" and examined by forensic scientists.
New details were given yesterday about how the ruthless gang, believed to number six, kidnapped Colin Dixon, 51, the manager of the cash depot, along with his wife, Lynn, 45, and eight-year-old son, Craig.
Mr Dixon, of Herne Bay, Kent, helped the robbers get into the depot after he and his family were threatened at gunpoint during a six-hour ordeal. The gang tied up 14 security guards and other members of staff, along with the Dixon family, in the depot, loaded a lorry and escaped early on Wednesday. They took between £25m and £50m, although the exact figure will not be known for days.
Police want to trace the movements of a red van, formerly owned by Parcelforce, abandoned at the Hook and Hatchet pub in the village of Hucking. They believe it may have been used in the abduction of Mrs Dixon, who remembers having been inside the vehicle at some stage.
Police said the raid was committed with "military precision" by professional robbers using extreme violence. Detectives believe the gang may have fled abroad with their haul, possibly via the Channel Tunnel.
Mr Leppard said all ports were on special alert, footage from closed-circuit television was being examined, and police forces abroad had been contacted. He said officers were working with police in Northern Ireland to investigate any links with the £26m Northern Bank robbery in Belfast, which also involved the kidnapping of families of keyholders.
One hundred detectives and staff from Kent police are investigating the Securitas robbery. The gang knew precise details of the movements of the security manager and his family, as well as the layout and workings of the warehouse, leading to the belief that they had inside help.
The police are also liaising with the National Crime Squad and the Metropolitan Police who have provided details of the country's leading armed robbers. Mr Leppard said: "This is organised crime at its top level. This was planned and executed with military precision. This is a terrifying crime committed by professional and organised gangsters." He said the manager's wife and son suffered a "terrifying ordeal", and added: "This is the most traumatic part; a woman and her young son were held at gunpoint in a vehicle for up to six hours and driven around."
Mr Dixon and his family are said to be traumatised. The manager was described by a neighbour in Herne Bay as a "person of integrity". Michael Pout said: "They were the sort of family anybody would like to have living next door. There is concern for them. It is not the money, as long as they are OK and alive. The money makes the headlines but that is not important."
Craig Dixon, who is nine today, was described by his teacher as a "normal and pleasant boy" with "very supportive" parents.Reuse content