A major test case, which could extend the liability of industry to include work-induced lung diseases, is now in progress before a High Court judge in Wales and is expected to go on well into next year with further sittings in Sheffield and London.

The action has been mounted by a group of eight former pitmen and widows of pitmen and is backed by Nacods, the pit deputies' union.

At present British Coal, which is being sued, only accepts a link between the coal miners' killer disease, pneumoconiosis, and coal dust.

However, the company is contesting the case currently being heard at the High Court in Cardiff by Mr Justice Turner.

If it succeeds it could open the floodgates to tens of thousands of claims by miners suffering from diseases such as asthma, bronchitis and emphysema, which the miners' group claims can also be dust related. British Coal's QC, Nicholas Chambers, has argued that the case being put forward on behalf of the claimants is "confused" and "unacceptable".

But the miners, represented by coordinating solicitors Irwin Mitchell, claim that exposure to coal-dust has caused numerous cases of respiratory illness.

If the current claims succeed then it is estimated that a further 55,000 ex-miners could pursue similar claims.

However, an early result is unlikely. When the hearing at Cardiff ends the case will adjourn until a further sitting, this time in Sheffield, where more ex-miners from northern coalfields will give evidence.

Then the case will move to London next year for experts to give their evidence. The whole action is expected to take at least six months.

The case is being handled for British Coal by Nabarro Nathanson partner Gareth Watkins.