A gang of robbers targeted a delivery van carrying "high value computer equipment" near Heathrow Airport on Monday night by setting up a fake police checkpoint.
The four men, dressed in high visibility jackets, attacked the van driver and his companion with CS gas and threatened them with a taser at 11.18pm, having laid their trap up on Stanwell Road near the junction with the A30 at Heathrow.
The robbers made off in the silver Transit van, which was later found abandoned in the Stanwell Moor area of Staines. The back doors had been forced and the computer equipment taken.
A Met spokesman declined to discuss what specifically the van was carrying.
"This was a well-organised and targeted attack aimed at a specific vehicle that the robbers knew would be carrying a high-value consignment," said investigating officer DS Ian Wilson.
The gang are also thought to have used a dark BMW 5 series and a dark Audi A4 saloon.
The heist is being investigated by Operation Grafton, a collaboration between the Met, Thames Valley Police and HMRC which battles organised criminals who target Heathrow cargo.
Wilson appealed for anyone with information to contact investigators on 020 8246 9972, or to speak anonymously to Crimestoppers on 0800 555 111. ®