A £2m reward has been offered by Securitas and a group of about 25 insurers led by Ascot Underwriting for the recovery.
The reward has been offered for the recovery of the £53m stolen in a recent raid and the capture and conviction of the armed gang responsible.
This is reportedly the highest ever reward offered for an insurance-related loss.
Since the raid on 21 February, almost £20m has been recovered.
David Edward of Ascot Underwriting said: “We knew we had to make an impact and set out to deliberately grab the headlines to encourage anyone with information that could be useful to the police to come forward.
