Ryan Preece was 27 when he was killed along with colleague Robert Simpson as they entered an underground chamber at a sewage pumping station near Swansea and were overcome by toxic fumes on October 10, 1996, the High Court heard.

Karen Stacey is to fight for a judicial review

Mr Andrew Nicol QC, representing Mr Preece's sister, Karen Stacey, said the tragedy happened after about three tonnes of a potentially lethal chemical had leaked from the nearby premises of Gower Chemicals Ltd into the main sewerage system.

And he challenged as "irrational" the Director of Public Prosecutions' refusal in November last year to bring corporate manslaughter charges against either Gower Chemicals or Mr Preece's employers at the time - Neath and Port Talbot County Borough Council.

Mrs Stacey, of Elmwood Drive, Briton Ferry, is asking Mr Justice Turner to open the way for a full judicial review.

Mr Nicol told the judge a jury at Neath Coroners Court had returned a verdict of unlawful killing after a lengthy inquest into Mr Preece's death in March and April last year.

Offences admitted

On October 19 1997, the County Borough Council had pleaded guilty to offences under the Health and Safety at Work Act and was fined £150,000 and ordered to pay more than £43,000 prosecution costs.

On June 15 last year at Swansea Crown Court, Gower Chemicals also admitted offences arising out of Mr Preece's death and was fined £100,000, with £33,000 prosecution costs, said Mr Nicol.

"Although both men regularly entered sewerage chambers in the course of their jobs, their employers - the council - had never warned them of the dangers of doing so, nor had they been provided 'with the essential equipment and training necessary to minimise risks," said Mr Nicol.

Mr Nicol accused the council of "a grotesque breach of safety requirements."

Reserved decision

Of Gower Chemicals, he said: "300 kilograms of chemicals disappeared down a hole which it was not even apparently appreciated was connected to the public sewer."

Mr Nicol said the DPP had failed to give the inquest jury's verdict "any or any sufficient weight" before deciding not to bring corporate manslaughter charges against either the council or Gower Chemicals.

But Mr James Turner QC, for the DPP, argued Mrs Stacey's complaints were based on "speculation" and had, in any event, been brought to court too late.