More than 27,000 children are thought to be members of criminal gangs but just a fraction are known to authorities, according to a major report.

Young people are increasingly preyed on by "ruthless" criminal enterprises as their "profile" means they are less likely to be known to police.

Analysis by the Office of the Children's Commissioner suggests that children in gangs are often faced with violence in a bid to keep them compliant.

The report, published on Thursday, suggests that the failings of authorities exposed by sex-grooming scandals are often repeated.

Its findings have now prompted calls for the government to designate child criminal exploitation as a "national priority".

Children's Commissioner Anne Longfield said: "The criminal gangs operating in England are complex and ruthless organisations, using sophisticated techniques to groom children, and chilling levels of violence to keep them compliant.

"At the moment it is too easy for them to succeed."

Children are often threatened with violence to keep them compliant. Credit: PA

Ms Longfield warned that "thousands" of children across England towns and cities were at risk of being groomed, adding that extra attention must be paid in protecting them.

“"However, I am worried that all the mistakes that led to serious safeguarding failings in relation to child sexual exploitation in towns and cities up and down the country are now being repeated," she said.

"Many local areas are not facing up to the scale of the problem, they are not taking notice of the risk factors in front of them, and they are not listening to parents and communities who ask for help."

Confidence in child safeguarding arrangements has been rocked by a string of sexual exploitation cases in recent years.

Analysis of crime survey data by suggests there are 27,000 children aged between 10 and 17 who identify as a member of a street gang.

A street gang is defined as a group of young people who hang around together and have a specific area or territory, have a name or other identifier, possibly have rules or a leader, and who may commit crimes together.

Researchers said that for some children gang membership represents little more than a loose social connection and not all young members are involved in crime or serious violence.

"For many children, involvement in these gangs is not a voluntary act," the report added.

"In some areas children are considered members of a gang based purely on their location, their family or their wider associations."

Gangs have sought to diversify their recruitment as police have become better at spotting "traditional" members, the paper found.

It said techniques for recruiting children are similar to grooming for sexual abuse, starting with "inducements".

In one case, there was said to have been a "written manual" setting out a clear timeframe for entrapment.

The commissioner's office raised particular concerns about an estimated 34,000 children who are in, or on the periphery of, a gang and have experienced violence in the last 12 months.

Gang members may become known to local children's services or the criminal justice system, according to the report.

Only a fraction of children affiliated with gangs are thought to be on the radar. Credit: PA

It calculated that only 6,560 children involved in gangs are known to authorities.

"In reality the under-identification is likely to be greater still," the report said.

The findings come amid intense concern over youth violence, and knife crime in particular.

Earlier this month it was disclosed that the number of fatal stabbings in England and Wales had risen to its highest level since records started more than 70 years ago, with increases most pronounced among younger age groups.

The assessment chimes with warnings about "county lines" gangs that exploit children and teenagers to run lucrative drug supply networks.

A government spokeswoman said: "We are committed to protecting vulnerable children by cracking down on the ruthless gangs that seek to exploit them and by offering them the support and skills they need to lead lives free of violence.

"That is why we launched the Serious Violence Strategy, which puts a greater focus on early intervention alongside a tough law enforcement response.

"We have proposed a new statutory duty on partners across education, social services and health to work together to tackle violence as part of a public health approach, and are providing £220 million to support children and young people at risk of becoming involved in violence and gangs."