A woman has been arrested by detectives investigating the deaths of three patients at Stepping Hill hospital, Greater Manchester Police have said.

This afternoon the Nursing and Midwifery Council said it had received confirmation from the Greater Manchester Police Force Intelligence Branch and Stockport NHS Foundation Trust that “registered nurse Rebecca Jane Leighton has been arrested and is being questioned by the police”.

In a statement, the nursing regulator’s chief executive Dickon Weir-Hughes said: “We have commenced fitness to practise proceedings with a view to suspending her from the register as quickly as possible. 

“The NMC is the only organisation with the authority to protect the public by suspending a nurse’s registration while they are under investigation.

“As this is now an open fitness to practise investigation, we are unable to provide further comment about the details of the case at this time.”

In a short statement made this morning, Greater Manchester Police Police said: “A 26-year-old woman was arrested on suspicion of murder. She remains in police custody for questioning. Inquiries are continuing.”

Yesterday the chief executive of Stockport Foundation Trust, which runs the hospital where the deaths of three patients are under police investigation, said the deaths had resulted from a “criminal act”.

Chris Burke told a press conference at Stepping Hill Hospital that “malicious intent” was behind the deaths, as a fourth patient was revealed as being critically ill.

The patient, a man in his 40s, now forms part of the huge police investigation at the hospital with 60 detectives focusing on people who either work at or visit the site in Stockport.

Police said they were concentrating on 14 patients in total who may have come to harm, including the three who died.

Mr Burke said: “This is a criminal act, perpetrated by someone with malicious intent. We do not believe it could have been anticipated.”

The unexplained deaths of Tracey Arden, 44, George Keep, 84, and Arnold Lancaster, 71, who all died at the hospital in Stockport, are already part of the police investigation.

They are being linked to the deliberate contamination of saline solution. Insulin was found in a batch of 36 saline ampoules in a storeroom close to ward A1 of the hospital.

Stockport Foundation Trust chief Mr Burke said security had been ramped up and there were now daily review meetings between senior police and NHS managers.

Inquests into the deaths of Ms Arden, Mr Lancaster and Mr Keep were briefly opened by South Manchester Coroner John Pollard at Stockport Coroner’s Court.

They were adjourned until a later date at the request of Superintendent Julian Ross, of Greater Manchester Police, who is leading the inquiry into the deaths.

Police also announced today that a product containing saline solution found damaged in the maternity ward at Stepping Hill Hospital was not contaminated.

“Preliminary tests confirmed no trace of any substance and officers are working to establish whether the damage to the product is accidental or deliberate,” Greater Manchester Police said.