Scotland Yard detectives investigating a multi-million pound robbery at Heathrow Airport have recovered �1m in cash.

In addition, 12 people were arrested in a number of dawn raids on Tuesday morning on houses across London.

Ten men and two women were taken away by the Flying Squad to three undisclosed police stations.

They face questioning about the robbery in March in which two men escaped with $3.2m and other currency after hijacking a security van.

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Police teams have carried out a total of 16 searches at homes and businesses across London.

No charges have been brought.

Those arrested, all aged between 21 and 37, are being held on suspicion of conspiracy to steal and conspiracy to money launder.

Detective Chief Superintendent John Coles said: "The arrests are the culmination of a two month pro-active operation by the Met's Flying Squad.

"This robbery was one of the biggest to take place in recent years."

'Inside job'

The raiders struck on 19 March as cash from a South African Airlines flight was being transferred to a security vehicle in the "airside" area of Terminal 1.

The van driver told police he was forced to drive out of the airport with a knife at his throat and the robbers then transferred the cash boxes to another van.

The robbery came five weeks after two men got away with �4.6m worth of foreign currency in a raid on a security van at Terminal 4.

Police said initially they believed that raid, in which two robbers were armed only with plastic wrist ties, may have been an "inside job".

Afterwards, Transport Secretary Stephen Byers, who is responsible for aviation security, demanded an "urgent report" into the implications as it took place during a period of heightened security after the 11 September terror attacks.