Plant and equipment cover could disappear if it does not become more profitable for insurers, National Plant and Equipment Register manager Tim Purbrick has warned.
He said insurers were regularly hit by unexpectedly high claims, fraud and theft.
"Underwriters ask clients to provide a valuation of their equipment fleet, then calculate the premium based on what the client is telling them the fleet is worth," he said.
"This has allowed some clients to adjust the valuation to the premium."
Purbrick said insurers' lack of detailed knowledge of the fleet meant they could be more easily defrauded.
He said insurers were becoming disenchanted with unprofitable sectors, including plant and equipment.
"If the underwriters and claims staff can't bring these accounts to profitability, senior management will have to look very carefully at whether they want to be in this business area."
The Association of British Insurers is considering Home Office advice that insurers make registration with the register a prerequisite of cover.