There is enough evidence to bring criminal charges over the deaths of at least 450 people at Gosport War Memorial Hospital given unnecessary doses of opiates, according to the detective who investigated the case.

Steve Watts, former assistant chief constable at Hampshire Constabulary, led the investigation into 94 of the deaths and said he believes prosecutions could have been brought when he handed evidence to the Crown Prosecution Service in 2005.

“I think it’s strong enough now, I think it was strong enough then, and I think there was an overriding public interest in doing so,” Mr Watts told the BBC’s Panorama – in an episode which aired on Monday evening.

Last year, an independent inquiry revealed as many as 656 patients died because of a “culture of hazardous opiate prescribing” on the wards that developed under Dr Jane Barton, a GP and clinical assistant.

Families who lost loved ones at the hospital have been calling for those responsible to be prosecuted to the full extent of the law, and expressed frustration that the scale of the scandal has not led to more immediate action.

Mr Watts added: “I knew what the response of the families was going to be, I knew what the response of the public was going to be and I recall talking to the prosecutors and saying that this will end up in a public inquiry and eventually I think the matter will go before a court.”

While the CPS considered charges of manslaughter and murder against Dr Barton and nurses who administered the lethal doses of opiates, it thought they were unlikely to achieve a conviction at the time.

Investigation of the new findings is being led by Kent and Essex Police, after the inquiry found Hampshire Police had been “consistently poor”, but families fear the CPS may again stop short of giving them justice.

'We demand justice': The families at the heart of Gosport scandal Show all 4 1 /4 'We demand justice': The families at the heart of Gosport scandal 'We demand justice': The families at the heart of Gosport scandal Charles Farthing's stepfather Arthur Cunningham died at Gosport. Farthing told the inquest that Arthur was 'out of this world and I thought straight away they must be killing him, because my mum had been given a syringe driver just before she died of cancer in 1989.' BRIJESH PATEL 'We demand justice': The families at the heart of Gosport scandal Maggie Ward's mum Norma Windsor died on her 69th birthday after 10 days of 'rest and recuperation' at Gosport. Ward says: 'There should be justice. We don't understand why the deaths at Gosport aren't as important as the Shipman murders.' BRIJESH PATEL 'We demand justice': The families at the heart of Gosport scandal Iain Wilson's dad Robert's last words were 'help me son, they're killing me'. Wilson says: 'Every time I'm told 'no' by the coroner or the police or the GMC, it just makes me more determined to keep searching for the truth. I have to get justice for him.' BRIJESH PATEL 'We demand justice': The families at the heart of Gosport scandal Cindy Grant (pictured here with her brother) says of her father Stan Carby's death: 'Dad was taken from us and mum died in 2007 without knowing what happened. We have to see it through for her.' BRIJESH PATEL

In the wake of the independent inquiry report in June, the CPS prosecutor Rene Barclay released a statement saying the report was still not enough to bring prosecutions.

The CPS later clarified it had not seen all the papers that had been unearthed and is awaiting the conclusion of the police investigation.

At a meeting with patients, CPS and the police in January, Gillian Mackenzie, who was the first person to go to the police with concerns about the death of her 91-year-old mother in 1998, said she challenged Mr Barclay to look at murder charges.

“I personally went to town with him because he was still talking about [charges of] corporate liability and perhaps gross negligence manslaughter,” Ms Mackenzie said.

“I said I was appalled he was still thinking in those terms… once or twice may be gross medical manslaughter – it is not 456 times.”

Bridget Reeves, whose 88-year-old grandmother Elsie Devine died at Gosport in 1999, also attended the meeting.

“At the end of the meeting the bishop stood up and was very forthright, he said there was absolutely new evidence in the report and agreed with the families – he couldn’t see where the CPS was coming from,” she said.

“The CPS expert Professor [David] Black said my grandmother had multiple myeloma, that was one of the reason’s they thought the drugs were appropriate.

“But it’s clearly pulled out in the report that she didn’t have multiple myeloma – so that’s new evidence.”

Stephen Lloyd, Ms Mackenzie’s MP for Eastbourne and Willingdon, has been supporting the calls for prosecutions in the wake of the report’s findings.

GoSport hospital deaths: Dr Jane Barton statement

“I believe the relatives deserve their day in court, and I believe Dr Barton should have to defend herself, one way or other, in that court.”

Dr Barton was found guilty of “serious professional misconduct” by the General Medical Council in 2010 but was allowed to keep her license and retired shortly after.

She has since said she was “doing her best for patients” under increasingly pressurised circumstances and that senior consultants were aware of her prescribing.

The CPS said it had given guidance on what charges might be possible but would not rule anything out until the police investigation had concluded.

A spokesperson said: “If following completion of their review and any subsequent investigation the police refer the case to us for a fresh charging decision or a reconsideration of any previous charging decision, then we will review the case.