The father of a toddler who died after suffering a serious sexual assault may never be charged with a crime because of a series of failings by police officers dating back to the day of her tragic death.

Detectives let vital evidence from Poppi Worthington’s family home be lost, decided not to make immediate arrests and did not question witnesses for months after she died in 2012.

A coroner told a second inquest into the 13-month-old’s death that he could not deliver an “unlawful killing” verdict because of a lack of evidence.

The Crown Prosecution Service (CPS) said it would carefully consider David Roberts’ findings that Poppi was sexually assaulted shortly before dying from asphyxia in her father’s bed.

“This is not the same as reviewing the case,” a spokesperson cautioned. “What we are doing is considering the coroner’s decision in order to establish whether it might provide the basis for a review, taking account of the fact that the evidence has been considered by prosecutors on three previous occasions.”

The first was in March 2015, when the CPS decided there was insufficient evidence to secure a realistic prospect of conviction on the basis of information passed over by Cumbria Police.

After a family court judge ruled that Poppi had been sexually assaulted the following year, another prosecutor came to the same conclusion and a third review turned down an appeal under the Victims’ Right to Review Scheme in June 2016.

Poppi Worthington's father is rushed into court

The new inquest held in Kendal, Cumbria, was told that Poppi was heard screaming at her family home in Barrow-in-Furness on 12 December.

Mr Roberts ruled that, at some point after 2.30am, she was taken from her cot and sexually assaulted, although it was not the cause of her death.

The toddler, who was suffering from an upper respiratory tract infection at the time, later died from asphyxia caused by the illness and an “unsafe sleeping environment” in her father’s double bed.

“When the father awoke he discovered that Poppi was no longer breathing and shortly before 5.56am, he took her downstairs in an unresponsive state,” the coroner said. “I find that, in fact, she was dead at that point.”

Paul Worthington has denied any wrongdoing and his lawyers entered submissions saying there was not enough evidence to conclude the toddler was unlawfully killed.

In a statement, they added: “Mr Worthington is considering his options following the coroner’s conclusion and we are advising him not to say anything further at this point.”

Poppi’s mother called for him to be prosecuted after he refused to answer 252 questions at the inquest using a rule to stop witnesses incriminating themselves.

Mr Worthington described his daughter as a “bully” at one hearing and would not explain how her DNA came to be on his penis, refusing to recount the hours leading up to Poppi’s death.

A sketch of Poppi Worthington's father Paul Worthington giving evidence at Kendal County Hall in Cumbria (PA)

Her mother’s lawyer, Fiona McGhie, urged the CPS to “take another look at the case” but a U-turn on its previous decisions looks unlikely unless Cumbria Police provide fresh evidence.

“The past five years have been a complete nightmare for her,” she added. “Not knowing what happened to Poppi on that day, and knowing that there were evidence gathering failures by the police in the very early stages of the investigation has made things even worse.”

The Independent Office for Police Conduct (IOPC) found that police officers in charge of the case had a case to answer for gross misconduct after uncovering a catalogue of failures.

The case started falling apart within hours of Poppi’s death on the morning of 12 December 2012.

Police should have closed off the entire house to secure any potential evidence, the watchdog found, but instead sealed only one bedroom and allowed the couple’s remaining children and family members access.

Officers supposedly guarding the property let the last nappy worn by Poppi to be thrown away by a relative who found it on the sofa.

The IOPC said it “had the potential to be a crucial piece of evidence in the investigation”, adding: “The nappy was never recovered and its value remains unknown.”

A laptop Mr Worthington used to watch pornography was also never seized by police, after he claimed he had sold it on to a friend.

When officers interviewed Mr Worthington, they “did not have any suspicions despite the fact that the father appeared to be getting things wrong and changing his story and there were inconsistencies between the two accounts provided by the parents”, the report found.

Instead of seeking to investigate Poppi’s death as a potential crime, an officer put his responses down to the fact it was a “traumatic situation” and did not raise the alarm.

Police were hampered by opposing findings by two pathologists who conducted a post-mortem on Poppi.

One was concerned she had sustained injuries from serious sexual abuse, repeating the finding in a phone call to police, but the other claimed they may have been caused by a medical condition.

Senior officers failed to challenge the mixed findings, which did not provide a cause of death and then had a break, telling investigators afterwards: “It was a real shame that there was a weekend involved…for two of those days nothing was done because it was a weekend and we were off.”

The IOPC raised concern over the failure to immediately treat Poppi’s death as a criminal investigation, with Mr Worthington asked to go for tests but the results not sent for analysis for months.

He was not arrested until August 2013 but investigators said the urgent need to protect Poppi’s siblings alone would have been ample reason to detain him immediately after her death.

By that point, “vital evidence” had been lost and the CPS said it could not proceed with charges.

The IOPC said that although there were two legitimate lines of investigation into whether Poppi’s injuries were the result of abuse or a medical condition, there was a disproportionate “focus on establishing a natural cause of death and the investigation was not conducted thoroughly, with opportunities being missed from the start”.

Two officers were found to have cases to answer for gross misconduct, but one retired before the watchdog released its findings and the second left Cumbria Police after being demoted as a penalty for “incompetency”.

The force said it had referred itself to the IOPC for investigation after Poppi’s death and apologised to her family.

A spokesperson told The Independent the decision not to launch a criminal investigation was “made by the officer in charge on the day, based on their interpretation of the facts and knowledge of available powers”.

He added: “An investigation was taking place from the outset but the constabulary accepts that the pace and scope of this investigation in the early stages was not of an acceptable standard…the constabulary are aware that these deficiencies were a factor in the CPS decision not to bring charges.

“The chief constable has, a number of times, unreservedly accepted the criticisms contained within the report and offered a heartfelt apology to Poppi’s family.

“The investigation fell well short of the standard that could, and should, have been expected.