A landmark Supreme Court ruling handed down yesterday (28 March) means insurers could face hundreds of millions in claims from sufferers of mesothelioma, a cancer caused by exposure to asbestos dust.

By a majority of four to one, the Supreme Court ruled that the insurer indemnifying an employer at the time of exposure of their staff to asbestos – known as the trigger period – was liable for subsequent damages claims, not the insurer providing cover at the time mesothelioma develops.

The dispute handed roles to a clutch of firms and QCs, including DLA Piper insurance litigator Leon Taylor for appellants BAI and Independent Insurance Company, and Irwin Mitchell personal injury partner Helen Ashton, who represented respondent Ruth Durham. Durham acted as lead claimant in the case in memory of her father, Leslie Screach, who died in of cancer in 2003 after work-related exposure to asbestos in the 1960s.

Roger Stewart QC and Stephen Robins of 4 New Square were instructed for BAI v Durham and BAI v Thomas Bates and Son, acting against Devereux Chambers' Colin Wynter QC and Outer Temple's Alison McCormick for Durham, and Exchange Chambers' Edward Bartley Jones QC with Exchange Chambers' Digby Jess for Thomas Bates and Son.

It is estimated that the ruling will leave the insurance industry to pay out in the region of £500m-£5bn. However, the Association of British Insurers (ABI) and much of the insurance industry had already supported the stance of paying out from the point of exposure. The ABI, which has sought to distance itself from the insurance firms that fought the claim, yesterday welcomed the ruling.

In total, nine appellants and four respondents were involved in the ruling, represented by QCs from multiple chambers including Devereux, Outer Temple, South Square, Blackstone and Crown Office Row.

The ruling – the culmination of a six-year legal battle – was handed down by Lords Phillips, Mance, Kerr, Clarke and Dyson, with Mance delivering the main judgment.

DLA Piper's Taylor commented: "Today's ruling puts an end to years of uncertainty for everyone, including sufferers and their families, but also policyholders and insurers who had sought clarification from the court, as the justices ruled in a clear majority that insurers who covered employers at the time they exposed their employees to asbestos must pay out.

"Lord Mance's judgment is a model of clarity and should draw a line under the problem in a way which the earlier Court of Appeal decision failed to do," he added.

The ruling partially overturns a 2008 Court of Appeal judgement, which held that some insurers were liable for 'trigger' claims while others were not, depending on the wording of the contract. The Supreme Court's decision is final, with no right of appeal for insurers or other interested parties.

Irwin Mitchell's Ashton said: "There have been repeated challenges to the entitlement to compensation of the asbestos victims by the defendants in this case … This long-awaited judgment provides clarity, consistency and comfort for mesothelioma victims and their families."

Claims put on hold until the outcome of the Supreme Court ruling will now need to be processed by insurers, with Taylor saying it is likely those involved in the ruling will be ordered to pay the claimants the insurance proceeds "within a matter of weeks". Other claims may take longer to finalise.

Click here for the full judgment.