Vulnerable children are being left at risk of sexual abuse from within their family by the failings of state agencies tasked with keeping them safe, according to a damning report into child protection.

It warns that shortcomings in police investigations, management of offenders and treatment of children showing worrying behaviour are allowing some perpetrators to continue their abuse unchecked.

Failures to fully investigate abuse for as long as a year left some children at risk, while there were also cases in which key agencies were unsure of where a recently released offender was living.

Investigators also raised concerns that contact between an offender and an abused child was sometimes in the hands of vulnerable women. In some cases, the women themselves had been the victims of bullying and coercive behaviour.

The alarming findings are contained in a major report by some of the country’s leading inspectorates, to be published this week. It examined how well the children’s social care, health, youth offending, police and probation services were working together to protect children abused by people in their family circle. Leading figures last night described the findings as a wake-up call.

Amanda Spielman, Ofsted’s chief inspector, said: “It’s unacceptable for children to be left at risk by the very agencies supposed to protect them. Too often, children abused at their family home are repeatedly victimised, while perpetrators are allowed back on the streets unchecked.

Too often children abused at their family home are victimised, while perpetrators are allowed back on the streets Amanda Spielman, Ofsted chief inspector

“It’s disappointing that we’re still seeing agencies working in silos, and professionals lacking the confidence to challenge decisions that aren’t in children’s best interests. There is a striking lack of grip – nationally and locally – on this endemic problem. This has to change.”

The report was drawn up by Ofsted, HM Inspectorate of Constabulary and Fire & Rescue Services, the Care Quality Commission and HM Inspectorate of Probation. It examined the protection of children from sexual abuse within the family in six local authority areas: Bracknell Forest, Cornwall, Derby City, Islington, Shropshire and York.

While inspectors found “pockets of good work”, the study also uncovered “deep concerns” about how some cases were being treated. Failings include lengthy delays of up to a year in arresting or questioning suspects, and in the forensic examination of digital equipment.

In one case, police failed to even interview a family member until four weeks after a child had disclosed that they had abused her. The perpetrator was not arrested, meaning that the child was also not protected by bail conditions that could be placed on them. Inexperienced officers were also given complex cases, which saw suspects left in the community without any restrictions placed on their movements.

Issues were also identified over the treatment of offenders as they leave prison. Plans were not always in place to manage their release, while the lack of suitable housing made it hard to limit their contact with children.

Some professionals failed to use legal “prevention orders”, which can limit where an offender lives, works and who they associate with, as a tool to prevent harmful sexual behaviour. In one area, police officers did not visit some convicted abusers at home, meaning they could not be sure where they were living. “This presents a huge risk to children,” the report concludes.

It warns that too much responsibility is placed on mothers to manage the contact between abusers and their children. It criticises the use by some agencies of written agreements, drawn up on a voluntary basis, as a method of safeguarding children. The report warns that the use of such agreements places “unrealistic expectations” on the parent’s ability to keep the child safe.

In one alarming case, a written agreement was used despite the mother not believing that the perpetrator had committed an offence. In other cases, mothers who had themselves been subjected to coercive control and domestic abuse were being expected to manage contact between their children and offenders.

Issues have also been identified over the treatment of children who exhibit worrying sexual behaviour. Investigators found that, too often, professionals focused solely on the child’s behaviour, without considering whether children themselves could be victims of abuse.

The report concludes that little progress has been made since England’s Children’s Commissioner examined the issue of child sex abuse within families in 2015. The study by Anne Longfield, who is still in post, called on the government to “make tackling this very difficult and complex problem a priority”.

“A system which waits for children to tell someone cannot be effective,” it warned. “It is clear that professionals working with children, and the systems they work within, must be better-equipped to identify and act on the signs and symptoms of abuse.”