The level at which children are being exploited by criminals in Britain is “almost back to Victorian times”, a police chief has said.

Chief Constable Shaun Sawyer said a reduction in state-run youth services has left a void between the “school gate and the front door” which criminals are exploiting.

In an interview with the Guardian, he also called for boys who are being exploited to be treated as victims, rather than criminals – in the same way young girls are.

Mr Sawyer, who is the national policing lead for modern slavery, told the newspaper: “For these children they are almost back to Victorian times and are being criminally exploited. These kids are looking for family and security. This is the vacuum of youth diversion schemes.

“For understandable reasons of austerity, state youth services have been vacated. This gap of youth provision between the school and family is the void that the exploiters are filling.”

A Government spokesman said it was committed to ending “the abhorrent exploitation of children” and to prosecute criminal gangs putting them at risk.

Many youngsters who were victims of modern slavery and human trafficking were British nationals, Mr Sawyer told the newspaper, with the figure up 73.7% from 2018 at about 726 people.

Mr Sawyer, who is the Chief Constable for Devon and Cornwall Police, said criminal exploitation driven by drug gangs was one of the biggest causes of modern slavery.

In a three-month period, 638 children under the age of 18 claimed to be criminally exploited, according to police figures seen by the Guardian. Mr Sawyer said the majority of these were due to county lines.

The term “county lines” refers to the mobile phone lines dedicated to taking orders from drug users, which are operated by criminals from big cities who have expanded into smaller towns.

They are known for forcing young and vulnerable people into crime by using them to act as drug runners.

Mr Sawyer said that while Prime Minister Boris Johnson’s promise of 20,000 more police officers would “make a dent” in the battle to protect children from exploitation, it “won’t stop the causes”.

He said: “One of the solutions to the causes is the gap between the dysfunctional home and the school.

“Youth diversion services need to be hard wired in. Child criminal exploitation, it’s all about family, creating feelings of security, self-worth and power. This gap between the school gate and the front door is where the exploiters are attractive to youngsters.”

Mr Sawyer also stressed the importance of seeing young boys who are being exploited as victims, rather than criminals.

“We accept that a 14-year-old girl does not make a choice to sleep with multiple men,” he said.

“I don’t think it is an informed choice to choose repeatedly to steal or deal drugs, and then hand over the profits.

“We’ve learned that girls who are exploited can be victims, but we seem unable or unwilling to learn the same lessons for boys where criminal exploitation is concerned.”

A Government spokesman said: “The Government is determined to end the abhorrent exploitation of children and young people and to stake out the criminal gangs that put them at risk.

“We established the National County Lines Co-ordination Centre which has resulted in more than 2,500 arrests and the safeguarding of over 3,000 individuals since its launch in 2018, and are investing in the people’s priorities and recruiting 20,000 new police officers over the next three years.

“We are supporting and investing in early intervention projects such as the Trusted Relationship Fund which works with local authorities to identify children at risk of abuse or exploitation, and have rolled out Independent Child Trafficking Guardians to key local authorities to provide support to child victims of trafficking.”