One in every hundred children living in care is abused every year in Britain, according to the most comprehensive study conducted into the issue.
The research by York University and the NSPCC is the first of its kind to uncover and analyse local authority records on abuse in foster and residential care.
Academics tracked abuse allegations – and their outcomes – between 2009 and 2012. They found that on average there are between 450 and 550 cases of proven abuse every year in foster care and between 250 and 300 cases of confirmed abuse a year in residential care.
In residential care the rate of substantiated abuse claims is significantly higher than for foster families, with an average of between two and three proven cases per 100 children. Steve McCabe, the shadow minister for Children and Families called the findings "shocking", saying that the conclusions of the report "suggests that the current level of supervision, scrutiny and inspection is woefully inadequate".
"It beggars belief that the Government can be planning to outsource even more children's services when these findings indicate that those which are already largely outsourced cannot be relied upon to provide the safe and secure environment that should be a priority for government," he added.
While the vast majority of foster carers do an excellent job in difficult circumstances, academics found that most abuse or neglect in foster care – more than 88 per cent – is perpetrated by carers. In more than a third of these cases the child was physically harmed and a further 11 per cent were sexually abused.
The examples detailed in the report include two cases where the sexual abuse of a fostered child was only discovered after the abuse of other children in the foster family prompted an investigation. One girl told how her regular foster carer had touched her inappropriately and tried to have sex with her. In another case, a male foster carer sexually abused two girls, claiming to be in a relationship with one of them.
Four cases involved the adult birth son of a foster family who was living in the home and abused young girls, three of these cases were sexual abuse over "a long period of time", some several years.
Some of the physical abuse documented took the form of a "spur of the moment" smack in a difficult situation but there were also cases of more serious deliberate harm. In one case, a child sustained several unexplained fractures during a foster placement and showed a lack of developmental progress dating back to the time it began. Emotional abuse made up a thirdof cases and neglect a further 17 per cent.
Tom Rahilly, of the NSPCC, said: "What this report shows is that while for the vast majority of children care offers a safe and loving environment, for a small minority we must do much better. The damage to children of being taken into care only to be mistreated by those entrusted by the state to protect them is immense."
He added: "More needs to be done to ensure that all children and young people in care are given a strong voice to share their experiences and provided with the help they need. Children must be allowed to see their social worker alone so they feel they have a safe environment to disclose concerns. This should remain in place even where placements have been on-going from many years. Access to advocacy services, such as that provided by the NSPCC, must be improved so children and young people have a constant and independent source of support."
More than two out of five foster carers in proven abuse cases had been subject to previous allegations – yet they were still caring for children. About a quarter of foster carers in these cases were looking after children who fell outside the age they were formally approved for.
More than 60 per cent of abuse victims in care are girls and the mean age of victims is nine. More than half of all substantiated allegations related to under-nines. Of those affected by a proven incident, 45 per cent were removed immediately from care, but almost a quarter remained where they were.
The researchers put in freedom of information requests to Britain's 211 local authorities on allegations of abuse in care and had responses from 156. They found evidence that warning signs were missed where children appeared to be settled in long-term placements but were in fact suffering ill-treatment.
Overall, there are between 2,000 and 2,500 allegations of abuse of children in foster care every year, around a quarter of which are substantiated. However, more than half of all unsubstantiated cases are not resolved as they cannot be proved either way. Four in 10 are proven to be false.
Robert Tapsfield, the chief executive of the Fostering Network, said: "We've supported the NSPCC to look at this important area of work.It is crucial to be clear about the difference between instances of abuse, instances of poor practice and accidents, and not simply to define them all as abuse as this report does. The report does highlight the importance of foster carers being well trained and supported and it emphasises the need to do more to identify those exceptional situations where children are ill-treated."
Alan Wood, the president of the Association of Directors of Children's Services (ADCS), said: "The process for being approved as a foster carer is rigorous – but no system can realistically be fail-safe. We must continually keep processes under review and ensure we have good and open dialogue between children and their social workers. We must do as much as is possible to ensure that foster carers receive high-quality training and support to ensure they can meet the needs of the children they are caring for."
Edward Timpson, the minister for Children and Families, said: "The report shows the majority of children in care are in stable, secure homes, but any incident of abuse or neglect is unacceptable. Where there is abuse or neglect, we are clear action must immediately be taken.
"We've introduced important safeguards to ensure children are protected, including improving the skills of social workers and toughening up the rules so councils and other agencies must have robust policies for protecting children.
"We have and we will take serious action where there is evidence to suggest they are failing in this."