The number of UK children being bullied on the internet has doubled this year, with more than one in three now victims.

In a British poll of 11 to 17-year-olds, 35 per cent reported that they have experienced cyber-bullying – compared with 16 per cent last year.

Four in 10 said they had witnessed others being picked on online – almost double the 22 per cent recorded last year.

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The study also suggests that thousands of teenagers, including many aged 15 or under, are using messaging service Snapchat and dating app Tinder every day.

Some parents even helped set their children up with accounts, prompting fears that they are unwittingly putting them at risk.

Internet security firm McAfee polled 2,000 UK children and 2,000 adults with at least one child aged under 18 ahead of the start of Anti-Bullying Week on Monday, and compared the findings with a similar study carried out last year.

The research indicated that there is a more relaxed attitude among increasing numbers of parents regarding the risks posed online.

Less than a third of parents (27 per cent) said they were worried about their child being the victim of cyber-bullying this year – almost halving from 45 per cent in the previous year, while two-thirds (67 per cent) of children are now allowed to go online without supervision – up from 53 per cent.

Andy Phippen, professor of social responsibility in IT at Plymouth University, said: “The responses from McAfee’s survey shows that there is a real gap between parental concern and the reality of what children face online.

“While it is encouraging to see that these conversations are happening, there are areas in which parents may not be completely aware of their children’s online behaviour.

“It’s now time for parents to take the conversations to the next level and become further educated on the social platforms that exist, what ages they are suited for and what type of behaviour they encourage.”

Around one in six of of the youngsters polled reported using Tinder every day, with almost half of those aged 15 and under.

Tinder users are shown other subscribers close to their location and must give a positive reaction to them in the form of a tick, and receive one back in order to start communicating.

It is open to those who are 13 or older, with under-18s only able to match with people in the same age bracket.