TV bosses were today accused of dealing a massive blow to crime fighting in Lancashire with an inaccurate storyline in hit police drama Prime Suspect.

Officials at Crimestoppers, the anonymous freephone tip-off service which provides information to police, are furious after it was portrayed asking for personal details and recording calls.

Their protests have now prompted an assurance from Granada that in future shows it will make clear information is accepted totally anonymously. The ITV show, starring Helen Mirren, attracted nine million viewers on Monday night and featured a tip-off to Crimestoppers on a murder.

The caller was asked for their name, the call was recorded and later traced.

But Lancashire Crimestoppers' officials have said this was inaccurate and totally against their ethos of guaranteed anonymity. And they fear the image of the service as being absolutely anonymous could have been "irreparably damaged."

Sue Arden, Crimestoppers development manager for the North West, said: "It would be a great shame if TV viewers now have the incorrect view of what underpins our work, which is anonymity.

"We value any information the community can provide about criminal activity in their neighbourhoods and we respect the caller's desire to provide that information without being known."

DC Andy Edwards, Crimestoppers co-ordinator for the Lancashire Constabulary, said: "Crimestoppers encourages people to come forward with information because they can give it anonymously and we would not want anything to jeopardise the public's confidence in this.

"Calls to Crimestoppers cannot be traced, phones used have no 1471 or 1571 facility and we would like to reiterate to the public of Lancashire how valuable the information received is. This is potentially very damaging. TV has a massive impact on people's lives as it flavours people's attitudes towards organisations.

"TV dramas need to make sure that their research is done properly. We will have to see if it has a negative effect when we look at the figures at the end of the month."

A spokesman for Granada said: "Granada understands the importance of anonymity to Crimestoppers. In Prime Suspect the anonymity of the service was stressed at the beginning of the call. But dramatic licence was taken with recording the call and requesting the caller's contact details.

"The production team has since spoken to Crimestoppers and reassurances will be made that forthcoming dramas will portray the service as totally anonymous."

Crimestoppers is a charitable trust and collects information on crimes from the public and passes it onto the police. To date this year, calls to Lancashire Crimestoppers have resulted in 176 arrests, £112,513 worth of property being recovered and £57,520 worth of drugs being seized.

In March, Crimestoppers Lancashire celebrated its best ever figures since its creation in 1991, with 10,000 calls received, and detectives view it as a crucial part of fighting crime.

Acting Detective Inspector Ian Critchley, from Blackburn CID, said: "Crimestoppers is a valuable tool. The public must be reassured thattheir identity at all times will be protected."

In the latest Prime Suspect, Helen Mirren's character, Detective Jane Tennison, put her career on the line and travelled to Bosnia to nail a murder suspect. The actress became a friend of Lancashire Constabulary's previous chief constable, Pauline Clare, after she became the first woman in Britain to take up the top post.