Machines were droped off at three addresses in Surrey in mid-January, after details of the contractor were used to place orders.
The haul includes a 17-tonne excavator worth £185,000, 3-tonne dumper, a 3-tonne hydraulic breaker, four ditching buckets and four loading buckets.
These items were delivered over the course of a week to addresses in Shepperton, Chertsey and Virginia Water, and then removed from the area.
The scam was exposed when the plant hirer which provided the machinery followed up with the groundworks contractor and found they had no knowledge of placing the order.
Police have released CCTV images of two men they want to speak to in connection with the incident.