The decision overturned a previous court ruling that companies should pay money to employees who had developed the condition as a result of being exposed to asbestos at their workplace.

The practice followed for the past 20 years by courts in these cases, which have awarded compensation of between 5,000 and 15,000 pounds to claimants for the anxiety that they might develop a serious illness, was "erroneous", Lord Chief Justice Nicholas Phillips said in the judgment.

Phillips said a pleural plaque "is neither visible, nor symptomatic and ... in no way impairs the bodily functions."

Employers, and their insurers, should therefore not be held legally liable if workers are found to be suffering from pleural plaques, even if it is clear they were the result of being exposed to asbestos at their workplace. Ruling on seven test cases, he said that, as litigation was expensive, it was "plainly desirable that claimants should not be permitted to pursue claims for trivial injuries".

The ruling does not affect the payment of compensation for more serious asbestos-related diseases, such as mesethelioma, a form of lung cancer directly connected to asbestos inhalation.

The court ruling may prevent more than 100,000 court cases involving pleural plaques or pleural thickenings being brought in future, which could have potentially cost insurers up to 1.4 billion pounds, according to research issued last year by the UK Institute of Actuaries.

"This judgement is dreadful and harms many of our members who have been exposed in their working lives to asbestos. We believe that people with pleural plaques should be compensated and we will fight on," Derek Simpson, general secretary of the Amicus trade union, said in a statement.

Norwich Union, part of Aviva, Britain's largest insurer, which was involved in the appeal, welcomed the ruling, while the Association of British Insurers said "it sets out that medical conditions that have no impact on health are not compensatable."

Other insurers who may benefit include Zurich Financial Services, Royal & SunAlliance and Lloyd's of London, which wrote liability policies for many British firms over the past 30 years.

The case will now go to the House of Lords after the Appeal Court took the unusual step of granting permission to appeal without the claimants having to ask the Law Lords directly.