Police have been ordered to investigate claims that Britain’s worst water contamination was the subject of a cover-up.

A delivery driver inadvertently emptied 20 tonnes of highly toxic aluminium sulphate into the wrong tank at a water treatment plant in Camelford, in Cornwall, 19 years ago. For weeks afterwards residents were assured that their water supply was safe, despite complaints that it had made skin peel, tea taste funny and had even turned the hair of one woman green.

The police investigation was requested yesterday by a coroner who is holding inquests for two residents from Camelford. Carole Cross, 58, and Irene Neale, 91, suffered rare forms of Alzheimer’s disease. Both were found to have high levels of aluminium in their brains, which is believed to be a cause of dementia.

Since the incident there have been three inquiries by the Department of Health, which concluded that it was unlikely there would have been any long-term damage to the health of those who drank the contaminated water. But dozens of residents have blamed the incident for chronic complaints ranging from depression to aching joints and memory loss.

Aluminium sulphate is highly acidic in solution and the contaminated water stripped other metals, such as copper, from the inside of water pipes to create a toxic cocktail.

Michael Rose, the Coroner for West Somerset, adjourned the inquests until the conclusion of the police inquiry. He said in a statement: “Tests have revealed that there may be a connection between at least one of these deaths and the earlier incident.

“In view of the serious allegations made in the media of a possible attempt to initially suppress the seriousness of the incident, I am asking the Chief Constable of the Devon and Cornwall Constabulary to hand me evidence gathered at the original investigation and also appoint a senior detective to look into the allegations of a possible cover-up.”

It has been claimed that the water board and the Government played down the seriousness of the incident from the start because of the possible consequences on the impending privatisation of the water companies.

Among the senior politicians who may be questioned by detectives is Michael Howard, the former leader of the Conservatives, who was the minister responsible for implementing the privatisation programme at the time.

Doug Cross, the widower of Mrs Cross and an environmental scientist, obtained a copy of a memo from a senior civil servant to Mr Howard under the Freedom of Information Act. The letter, signed by M. G. Healey, advised Mr Howard that the water board was concerned about the consequences of any investigation.

He wrote: “Those of the South West Board with a commercial background are deeply concerned by the investigation. They see the timing of any prosecution of the authority as being totally unhelpful to privatisation, while the prosecution of a board member in their view could render the whole of the water industry unattractive to the City.”

It was more than two weeks after the contamination that members of the public were first alerted. They were told that the water was safe to drink, despite some samples containing up to 6,000 times the recommended safe levels of aluminium.

Mr Cross, 70, who now lives in Cumbria, said that the dangers were known but that people were not warned properly.

He said: “People from the water authority took it on themselves to give advice to the public. The most outrageous thing they did was going on the radio and saying if you don’t like the taste, mix it with orange juice, which a lot of people did.

“For 19 years people in Camelford have been dying of strange things. The Government has known about scientific research as far back as 1989 that shows that some people are ‘super-absorbers’ of aluminium, and it can have very serious effects.

“I am not going to stop until I see these people brought to justice. People have died because of the short-term concerns of politicians.”

A spokesman for Devon and Cornwall Constabulary said that officers would interview politicians and civil servants if it was felt necessary.

Mr Howard said: “There is no suggestion in the memo that any investigation was obstructed because of water privatisation at all. There was no cover-up to which I was a party.”

Times Recommends

• The bright side of this winter rain
• Story behind the picture: Snow Leopard, 2008
• Times Charity Appeal: The Place2Be