Lives were "undoubtedly put at risk" when a health regulator ignored information supplied to it by the police about practising midwives, bereaved families have said.
The comments come after a "damning" report was released about the Nursing and Midwifery Council's (NMC) handling of the cases of midwives involved in the Morecambe Bay scandal where major care failures were linked to at least 12 deaths of mothers and babies at Furness General Hospital (FGH) between 2004 and 2012.
The report reveals how the NMC failed to act on information provided by the police for almost two years.
Poor record keeping, mishandling of bereaved families and lengthy and delayed investigations all feature in the Professional Standards Authority (PSA) report.
Prior to the report being released, the head of the NMC quit her role. Jackie Smith announced she was stepping down as chief executive and registrar on Monday.
The PSA "lessons learned" report concludes that the length of time taken to deal with the cases is "an obvious concern" - it took more than eight years between the first complaint being received by the NMC and the final fitness to practise hearing for one of the midwives involved.
The delay meant that midwives who were later suspended or struck off the regulator's register continued to practise.
Meanwhile the authors said that the NMC lawyers did not identify key issues from information in its possession, not only from the families involved, but also from the police.
Cumbria Police told the PSA: "We were really concerned that reports of the same midwives who we had the cases sitting in front of us were still practising at the hospital (sic)."
The police handed the NMC information highlighting concerns about the midwives they believed should be investigated.
The NMC appeared to have taken no action on the list for almost two years after being given the information.
"In our view, there was scope for the NMC to investigate the wider fitness to practise of the midwives concerned and the police expected them to do so at the time the information was sent," the authors said.
"We saw no evidence that the NMC considered doing so. This was an opportunity missed, given that some of the midwives identified by the police were subsequently involved in adverse events at FGH."
The NMC has admitted that its handling of the Morecambe Bay cases was "unacceptable" and has apologised.
But in a joint statement, Liza Brady, Carl Hendrickson and James Titcombe, who were affected by the events, said: "Today's report from the PSA details, for the first time, the truly shocking scale of the NMC's failure to respond properly to the serious concerns and detailed information provided to them relating to the safety of midwifery services at Furness General Hospital.
"We were particularly horrified that even when Cumbria Police directly raised significant issues, the NMC effectively ignored the information for almost two years.
"Whilst this was going on, serious incidents involving registrants under investigation continued, meaning lives were undoubtedly put at risk. Avoidable tragedies continued to happen that could well have been prevented.
"The NMC have been defensive, legalistic and in some cases, grossly misleading in their responses to families and others. This culture of denial and reputational management is reminiscent of the very worst of the culture our families have experienced over the years."
The report highlights how Mr Titcombe, whose son Joshua died after midwives missed chances to spot and treat a serious infection which led to his death nine days after he was born at FGH in 2008, was seen as "hostile to the NMC corporately".
The NMC monitored his Twitter feed and set up Google alerts on him.
The report also highlights how, when Mr Titcombe gave evidence to a fitness to practise panel the chair of the panel tried to force him to refer to his son Joshua as "Baby A" instead of using his name.
Mr Titcombe refused.
Overall, the NMC found concerns about the fitness to practise of the midwives proved in four cases.
Of those, one midwife was struck off 11 years after the first concerns about her practice arose, a second was struck off five years after she had retired and a third was suspended for nine months even though the panel found that there were no longer any concerns about the safety of her practice. The fourth was struck off having also retired.
"Further avoidable deaths occurred while the NMC were considering the complaints," the authors wrote.
Chief executive of the PSA, Harry Cayton, said: "What happened at FGH remains shocking, and the tragic deaths of babies and mothers should never have happened.
"The findings in the review we are publishing today show that the response of the NMC was inadequate.
"Although the NMC has made good progress with its technical handling of complaints and concerns, there remain cultural problems which it must remedy in order for the public to have confidence in its ability to protect them from harm."
Peter Walsh, chief executive of the patient safety charity, Action Against Medical Accidents, said: "The findings of the report are so damning, it can come as no surprise that the CEO of the NMC resigned this week.
"What is most shocking is the dismissive and disrespectful attitude towards the families who lost babies at the hospital, the lack of openness and honesty and the sheer incompetence of the NMC's approach."
A 2015 inquiry found a "lethal mix" of failures at the University Hospitals of Morecambe Bay NHS Foundation Trust led to the unnecessary deaths of 11 babies and one mother between 2004 and 2013.
Ms Smith said: "The NMC's approach to the Morecambe Bay cases - in particular the way we communicated with the families - was unacceptable and I am truly sorry for this.
"We take the findings of this review extremely seriously and we're committed to improving the way we communicate with families, witnesses and all those involved in the fitness to practise process.
"Since 2014 we've made significant changes to improve the way we work and as the report recognises, we're now a very different organisation.
"The changes we've made puts vulnerable witnesses and families affected by failings in care at the heart of our work. But we know that there is much more to do."
Barrow and Furness MP John Woodcock said: "This devastating report shows how local families were systematically obstructed and failed by an organisation whose conduct has brought shame on the proud and vital profession it is supposed to represent.
"The report shows how the organisation covered up and closed ranks to protect their own rather than treating grieving families with common decency.
"It is absolutely right that Jackie Smith has stood down as a result of these appalling revelations; her departure must herald a total transformation in culture at the NMC."
Health and Social Care Secretary Jeremy Hunt said: "We cannot bring back loved ones who have been lost because of what went wrong at Morecambe Bay but we can make sure parents and families never have to go through the same agony again.
"Whilst the NMC has improved since then, it clearly still needs a massive culture change so that families feel they are being genuinely listened to and not just made part of a process.
"Then and only then will the public be confident that learning has happened following a tragedy."
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