The NSPCC has called on the government to prioritise young people’s online safety after figures revealed police forces in the UK record an average of 22 cyber-related sex crimes against children every day.

The number of sexual offences against under-18s logged by police as having an online element doubled in four years to more than 8,000 in 2018-19, according to figures gathered by the children’s charity from 40 forces in England, Wales and Northern Ireland.

The most common age of the victim was 13, but 185 offences involved children aged 10 and under, including babies, a series of freedom of information requests revealed. The crimes include online grooming, sexual communication with a child, and rape.

In one typical scenario, a 13-year-old girl told the NSPCC’s Childline helpline that she had developed an online relationship with someone she met on Instagram. “He convinced me to send pictures of myself which was sexual. Now he has threatened he would share those pictures to my friends unless I send him more,” she said.

In another, a 14-year-old boy said he was sent a friend request by a woman in her 20s. “Later she video-called me and made me do sexual things. She later showed me a video of what happened and threatened to report me for masturbating if I didn’t talk to her,” he said.

“I feel so ashamed about what has happened and I’m too scared to tell anyone. I’ve blocked them but I feel so violated and scared. My end of the year exams starts tomorrow and I am struggling to cope with everything right now.”

Police began marking sexual offences with a cyber-flag whenever a crime involved the internet four years ago. In 2015-16, the total was 4,042, which rose to 8,244 in 2018-19, but according to the NSPCC, the figures may not show the true extent of the problem because some police forces are likely to underrecord the role of the internet.

According to the NSPCC findings, there was a wide variation in the number of offences cyber-flagged between forces across the country, with some logging hundreds of crimes while others recorded fewer than 20.

Speaking before the charity’s two-day annual conference in London, the NSPCC chief executive, Peter Wanless, said: “Behind each offence is a child suffering at the hands of sex offenders and, worryingly, we know these figures are the tip of the iceberg.

“Far too many children are drowning in a sea of online threats, so it’s now time for the next prime minister, whoever he may be, to cast out the lifejacket. He must hold his nerve and introduce an independent regulator to protect children from the risks of abuse and harmful content.”

The NSPCC conference will focus on the challenges of growing up online and include sessions on keeping children safe on the internet, including an “Interpol crime lab”, the dark web and how young people use the internet to form relationships.

The government is currently consulting on an online harms white paper, which outlines new laws to crack down on internet companies. Among the proposals under consideration is the introduction of an independent regulator to enforce a legal duty of care on technology companies to keep users safe on their platforms.