Girls are ganging up on boys in a new cyberbullying craze called “roasting”, a digital safety expert has warned.

The new bullying takes place via mobile apps such as WhatsApp, Instagram or Facebook, where girls pick on a boy and vent the most offensive abuse until the victim “completely cracks”.

This form of cyberbullying can also involve boys ganging up on girls or turning against each other in “very nasty” ways, experts have warned.

Teachers and parents at leading private schools have been warned to be aware of this new form of cyberbullying, as it tends to happen outside adult oversight because teenagers regard it as just one level up from banter.

The warnings followed research by non-profit motivational organisation dosomething.com, which suggested that girls are almost twice as likely as boys to be both victims and perpetrators of cyberbullying, as boys tend to be more involved in physical bullying.

Both boys and girls have killed themselves recently due to cyberbullying.

Charlotte Robertson, of online safety consultants Digital Awareness UK, said roasting was prominent among pupils of leading independent schools as well as in state schools across the country.

Speaking to The Daily Telegraph, Ms Robertson, whose company provides advice to independent girls’ schools, including those in the Girls’ Day School Trust (GDST), said: “Roasting is done under the guise of good humour, which is why it is so dangerous because it is often done among friends.