Insurers face a spate of plant theft claims resulting from the Olympic Games construction boom.
Tim Purbrick, manager of the National Plant & Equipment Register (TER), said: "We are in the crazy situation where £1m worth of plants a week is already being stolen but this could rocket as the Olympic development takes place, with ground breaking starting on the site next week.
Purbrick claimed a lack of registration was costing insurers heavily but they are too scared to make it compulsory.
He said: "There is no doubt they are already insuring stolen plant and don't know if claims have already been made on many items."
He said registration with the TER was cheap, costing plant owners a maximum of £100 for an unlimited number of machines. "We've made it affordable for everyone but only 20% of plant is currently on the register."
Purbrick added there was a lack of underwriting discipline in the plant sector, since policies was being provided often only on the basis of estimated values and without inventories.
He claimed the problem was further fuelled by patchy risk management and the fact that the same keys could often be used for the same model plant vehicles.
But some insurers insisted the problem was on their radars. Carl Gebhard, Zurich's head of construction and engineering, said: "The problem is escalating.
"Plant theft is estimated to be between £95m and £130m per annum. But, with knock on delays on site and rising insurance costs, the cost is estimated at over £600m."