A coroner has criticised a water authority for "gambling" with the lives of 20,000 people by not telling them for more than a fortnight about Britain's worst mass poisoning.

West Somerset Coroner Michael Rose criticised the South West Water Authority as he gave his verdict on the death of Carole Cross.

Mrs Cross, 59, died in 2004 from a rare disorder usually associated with much older people suffering from Alzheimer's disease. She had been living in the Camelford area of north Cornwall in July 1988 when the poisoning occurred.

She was one of 20,000 customers affected when a relief lorry driver mistakenly added 20,000 tonnes of aluminium sulphate to the drinking water at the Lowermoor treatment works.

The coroner recorded a lengthy narrative verdict in which he said there was a "very real possibility" that the ingestion of aluminium by Mrs Cross had contributed to her death.

The inquest, which first began in November 2010, heard that a post-mortem examination later found high levels of aluminium in Mrs Cross's brain.

The inquest was told that, for more than two weeks, South West Water Authority, which ran the treatment works, did not tell the public the cause of the poisoning and insisted the water was safe to drink. Many people reported rashes, diarrhoea, mouth ulcers and other health problems after drinking the water or bathing in it. The water became so polluted in the first few hours that customers reported hairs sticking to their body like superglue as they got out of the bath.

Customers flooded the switchboard of the water authority but were told it was safe and it has been claimed some were even advised to boil the water, which increased the levels of aluminium still further.

Mrs Cross, who lived on the outskirts of the town and later moved to Dulverton in Somerset, died in Taunton's Musgrove Park Hospital. She suffered from a rare neurological disease - cerebral amyloid angiopathy. Her husband, Dr Doug Cross, believes her exposure to high levels of aluminium during the incident caused her death 16 years later. Dr Cross, who now lives in Cumbria, did not attend the hearing in Taunton, Somerset.

Mr Rose said: "From July 9 for a few days Mrs Cross ingested a quantity of aluminium, precise measurements of which are not possible, because of the failure of the authority to ensure the public were encouraged to give urine and blood samples. I also regard the failure of the authority to visit every house after the incident to advise them to thoroughly flush their systems as a serious dereliction of duty. At the end of the day, I can say that the incident may either have contributed to or possibly caused Mrs Cross's death, but I do not have sufficient evidence to say so conclusively."

The Press Association, photo: The Vintage Skeleton