Up to seven new deaths are being investigated as part of a major probe at Airedale General Hospital.

It came after a senior nurse was arrested on suspicion of killing a 96-year-old patient at the site in Steeton near Keighley.

Today it was revealed that hospital bosses concerns' were only aroused after carrying out a "routine audit" of past deaths.

It is understood detectives are now examining hospital medical records stretching back two years - the time of the pensioner's death - and have singled out around half a dozen cases for closer attention.

If the suspicions prove founded, they are likely to extend their search well beyond this period.

While senior officers have refused to comment on their investigations, the Telegraph & Argus understands it centres on a handful of cases linked to the arrested nurse, who has not been named.

And one hospital source said the inquiry concerns her administering morphine to patients - a procedure she was not qualified or permitted to do.

It came as the head of Airdale's health watchdog said the revelations had "overshadowed" the hospital's reputation and called on the NHS Trust to restore patients' confidence.

On Thursday, the Telegraph & Argus revealed that the nurse was arrested in March on suspicion of the pensioner's manslaughter and the unlawful supply of controlled drugs. She has been released on bail and suspended from duties on full pay.

Hospital bosses confirmed they had called in the police after growing suspicious about the woman's death.

The probe - which has involved joint teams of police and nursing staff visiting former patients - is thought to focus on the arrested nurse's illegal administering of drugs to patients.

One senior member of nursing staff is supporting the investigation on a full-time basis.

John Godward, chief officer of the Airedale Community Health Trust, said patients would demand to know how the nurse was able to access and administer drugs when hospital rules strictly prohibited it.

He said: "I am devastated by this news and on behalf of the Airedale Community Health Council I offer our deepest sympathies to the relatives of the patients concerned.

"I also offer our sympathy to the Airedale NHS Trust and all staff who have the responsibility of caring for patients."

Mr Godward added: "It is inevitable that the reputation of this three star NHS Trust Hospital will be overshadowed by these events."

"The immediate concerns of the public and the patients will be to know that procedures have been put in place by the Trust and Department of Health to ensure that there can be no further recurrence of this type of thing by any member of staff in this hospital and throughout the NHS."

Mr Godard said the Trust must restore patients' confidence and added: "The Airdale NHS Trust has enjoyed the confidence of the local populations for many many years and the CHC hopes that they will be able to get back to this position quickly."

The Trust has assured patients they are not at risk and set up a hotline to answer their queries.

They can contact the service on (01535) 292505.