Householders could face potential bills of thousands of pounds if their property has been built on contaminated land.

From this month, local authorities begin testing land for harmful chemicals, under environmental measures introduced last year. If the original polluter cannot be found, current occupiers could face clean-up bills of up to £20,000.

Only those who can prove they are unable to pay will be exempt. Those who can afford to pay are not likely to be covered by their household insurance.

A number of insurers now offer additional cover to protect against contaminated land.