Ongoing analysis by the Historic Automobile Group shows that classic cars have risen in value by 430 per cent over the last decade, driven in part by wealthy investors choosing to put their money in cars rather than volatile stock markets.

Classic car owners are being urged by the British Insurance Brokers Association (BIBA) and they country’s largest specialist broker to review the true value of their car.

This can be done by looking at price guides and finding out what similar vehicles have been sold for.

Gerry Bucke, general manager at Adrian Flux Insurance Services, said: “We reviewed our classic car portfolio and noticed that a number of our customers had declared values that looked very low in today’s market. Some of the cars we cover have almost doubled in value since the owner’s last valuation.”

One Surrey man whose 1970 Porsche had been insured for £45,000 found that similar cars were selling on the market for between £80,000 and £100,000.

Classic car insurance works in the same way as home insurance, where the premium is partly based on the value of what is being insured. Owners could end up receiving only a percentage of a car’s true value if their insurance coverage level has not kept pace with the market.

Bucke said: “We can’t stress enough how vital it is to keep on top of market trends. We’d suggest reviewing valuations every year. Otherwise, if the worst happens, you could lose anything from a couple of pounds to tens of thousands.”

Graeme Trudgill, BIBA’s executive director, said: “It is great news for classic car owners that their cherished cars are appreciating so much, but it is vitally important to get the right valuation and to work with a classic car insurance broker like Adrian Flux to ensure the right cover.”