Geoff Barton, general secretary of the Association of School and College Leaders, said: “Most schools already forbid the use of mobile phones during the school day or allow their use only in limited and stipulated circumstances.

“We have lost count of the number of times that ministers have now announced a crackdown on mobile phones in schools. It is a non-policy for a non-problem.

“The government would be far better off putting its energies into bringing to heel the online platforms via which children are able to access disturbing and extreme content.”