Four insurance companies have been fighting to minimise payouts to 6,000 families who have a member who has died or is suffering from mesothelioma, a cancer resulting from exposure to asbestos. Once the court rules against the insurers, the compensation bill could be in excess of £600m. If you include future claims that will be brought, up to 25,000 families could be affected by the ruling, pushing the potential bill to £5bn.

The Independent on Sunday has been campaigning since 2009 for insurance companies to pay out to victims whose firms they supposedly covered when they were negligently exposed to asbestos dust.

The test case, which has gone to the High Court and the Court of Appeal, has been running since 2006 and is one of the most protracted in legal history. Most of the cancer patients affected by its ruling have now died, and it is their relatives who have been waiting on the result.

Asbestos exposure is the biggest killer in the British workplace, causing more than 4,000 deaths every year – more than road traffic accidents. The fibres can be in a person’s lungs for half a century before causing cancer, so that deaths in the UK are not expected to peak until 2016.

It has been known that asbestos dust caused fatal lung cancers since 1955, and its “evil effects” were observed in factories as early as 1898. Because of this, employers – or if they no longer exist, their insurers – are liable to compensate those needlessly killed by it.