The death of a four-year-old boy who was starved to death by his mother and left to decompose in his cot was not something police "could have reasonably been expected to predict or prevent", the police watchdog has found.

The Independent Police Complaints Commission (IPCC) has completed its investigation of West Yorkshire Police's conduct in relation to the death of Hamzah Khan, whose body was found in a cot at his home in Bradford in 2011, almost two years after he died.

Mother-of-eight Amanda Hutton, 43, was jailed for 15 years last year after she was found guilty of Hamzah's manslaughter and neglecting five of her other children.

At her trial it emerged that a range of agencies, including police officers, had contact with her family but no-one spotted the danger the children were in.

Today, the IPCC said in a statement: "The IPCC investigation concluded that Hamzah's death was not something West Yorkshire Police could have reasonably been expected to predict or prevent, and that it was the actions of a PCSO who made repeated and concerted attempts to speak to Ms Hutton that led to the discovery of Hamzah's body."

The commission said there had been no misconduct by officers but criticised the force for not referring itself to the IPCC at the time the body was discovered.

It said the fact it was not referred "hindered the IPCC in its obligation to carry out a prompt and effective independent investigation into West Yorkshire Police's contact with the family".

IPCC commissioner Cindy Butts said: "There was a clear public interest in enabling the Independent Police Complaints Commission to scrutinise the actions of West Yorkshire Police officers after the discovery of Hamzah's body in 2011.

"The fact that this was not reported to the IPCC until after a serious case review had been completed in 2013 meant that that process was completed without any independent scrutiny of police action."

Police had extensive contact with Hutton and her family over a number of years but mainly because she was a victim of repeated domestic violence.

Hutton's trial heard how Hamzah's father, Aftab Khan, raised concerns with officers after he was arrested for attacking Hutton but detectives told the court these were investigated and no problems were found.

Today, the IPCC said two officers chose not to make a referral to social services after specific allegations of neglect were made during this interview in December 2008.

But it said in its statement: "The IPCC found that a number of referrals had already been made, one of which was made only five days before the interview with Mr Khan. A further referral to social services could have been made but there was no requirement for the officers to do so."

A serious case review in Hamzah's case concluded that he was ''invisible for almost a lifetime''.

But that review was criticised at its publication by children's minister Edward Timpson, who expressed ''deep concerns'', saying it failed to fully explain ''missed opportunities to protect children in the house''.

The minister wrote to Professor Nick Frost, who chairs the Bradford Safeguarding Children Board, saying: ''I have deep concerns over the Hamzah Khan serious case review.

''In particular, I am concerned that it fails to explain sufficiently clearly the actions taken or not taken by children's social care when problems in the Khan family were brought to their attention on a number of occasions.''

Alcoholic Hutton was living in what the report described as ''breathtakingly awful'' conditions with five of her children as well as Hamzah's mummified remains when police entered her four-bedroom house in September 2011.

A jury at Bradford Crown Court found she had allowed Hamzah to starve to death in December 2009 and left his body in a cot with a teddy.

The remains were only discovered due to a rookie police community support officer's tenacious pursuit of a minor anti-social behaviour complaint because she knew something was wrong.

The family was known to all the main agencies, partly due to a long history of violence Hutton suffered at the hands of Khan.

But Hutton failed to co-operate with many children's services and the SCR found that Hamzah slipped below the radar and was invisible.

Ms Butts said today: "Nothing could have reasonably been done by West Yorkshire Police to predict or prevent this horrendous case of child neglect. In fact, it was the tenacity of one of its officers that led to the eventual discovery of his body."