At least 42 babies and three mothers may have died unnecessarily and more than 50 newborns suffered avoidable brain damage at a hospital trust, in what is believed to be the worst maternity scandal in NHS history.

A leaked status update on a review of clinical malpractice in the maternity service of Shrewsbury and Telford hospital NHS trust raised concerns about the high number of deaths and injuries there.

The review covers hundreds of cases between 1979 and 2017. The full extent of the scandal is expected to be found to be even worse as more cases are reviewed.

The trust apologised unreservedly to the families involved and said it was working to improve its maternity services.

The document, initially leaked to the Independent, found a “toxic” culture and substandard care, the paper reported on Tuesday.

Parents were frequently treated unkindly by staff and their concerns about treatment were dismissed, the report said. Staff got dead babies’ names wrong and in one case referred to a baby who had died as “it”.

The leaked document said a review carried out by the Royal College of Obstetricians and Gynaecologists (RCOG) in 2017 was inadequate, and it criticised the “misplaced” optimism of the regulator in charge in 2007, which said improvements could be made to the trust’s maternity services.

The inquiry, by was ordered by the government in July 2017, 15 months before the trust was put into special measures. It is being carried out by Donna Ockenden, a maternity expert.

In the document she wrote: “No apology will be sufficient or adequate for families who lost loved ones to avoidable deaths, or whose experience of becoming a parent was blighted by poor care and avoidable harm.”

In a statement on Tuesday, Ockenden said the leaked document appeared to be a confidential status update submitted last February, and a fuller investigation was continuing.

She said: “At the time I listened to the families involved in the maternity review who were very clear they wanted one single, comprehensive independent report covering all known cases of potentially serious concern within maternity services at the trust. My independent review team and I are working hard to achieve this.”

The initial scope of the inquiry was to examine 23 cases but this has now grown to more than 270. They include 22 stillbirths, three deaths during pregnancy, 17 deaths of babies after birth, three deaths of mothers, 47 cases of substandard care and 51 cases of cerebral palsy or brain damage.

Specific failures identified in the document include:

Babies left brain-damaged because staff failed to realise or act upon signs that labour was going wrong.

Inadequate monitoring of heart rates during labour and poor risk assessment during pregnancy, resulting in the deaths of some children.

Babies left brain-damaged from group B strep or meningitis, which can often be treated by antibiotics.

A baby whose death from group B strep could have been prevented after the parents contacted the trust on several occasions with their concerns.

Many families struggling to get answers from the trust around “very serious clinical incidents”, continuing to the present day.

A family being told they would have to leave if they did not “keep the noise down” when they were upset after the death of their baby.

Bereaved families routinely being advised “they were the only family” and that “lessons would be learned”. The report said: “It is clear this is not correct.”

The inquiry was launched after a campaign by the Stanton-Davies family, whose daughter Kate died shortly after birth in 2009, and Kayleigh and Colin Griffiths, whose daughter Pippa died shortly after birth in 2016.

Rhiannon Davies told the Independent that the leaked report showed the trust’s chronic inability to learn from past mistakes had “condemned my daughter to death”, adding: “How has this been tolerated for so long? It is horrific.”

Until now, Morecambe Bay, where there were avoidable deaths of 11 babies and one mother at Cumbria’s Furness general hospital between 2004 and 2013, was considered the worst maternity scandal in NHS history.

Bill Kirkup, who chaired the Morecambe Bay inquiry and has seen the leaked document, said he was shocked by its findings. “It is very disappointing we had the chance to learn general lessons from Morecambe Bay and it appears that unfortunately they have not taken the opportunity to act. So it is genuinely shocking,” he told the Guardian.

“The scale of it and the similarities to what had happened previously at Furness general hospital in Barrow – it is almost a carbon copy of the same features and apparently on a big scale. We don’t know the final scale but if there is potentially 43 unavoidable deaths, that is a big-scale problem.”

Paula Clark, the interim chief executive at Shrewsbury and Telford hospital NHS trust, said: “I apologise unreservedly to the families who have been affected. I would like to reassure all families using our maternity services that we have not been waiting for Donna Ockenden’s final report before working to improve our services. A lot has already been done to address the issues raised by previous cases. We still have further to go but are seeing some positive outcomes from the work we have done to date.”

She added: “We have not seen or been made aware of any interim report and await the findings of Donna Ockenden’s report so that we can work with families, our communities and NHS England/Improvement to understand and apply all of the learning identified.”

Judy Ledger, the founder and chief executive of Baby Lifeline, a maternity charity, said: “It’s devastating to hear of the dozens of avoidable tragedies that took place at the trust over the last 40 years, and the consequential heartbreak for those involved. The families have been forced to experience situations that should never be allowed to happen within the NHS.”