As students file out of their GCSE English lesson at Lostock High School in Manchester, I ask where they keep their smartphones.

“In here,” they all say, tapping and pointing to their blazer pockets.

The phones are on silent or switched off, and if they are heard or seen they are confiscated.

Most schools in England have a similar “no see, no hear” policy, although some are investing in lockable pouches which the students keep, or lockers where you can drop your phone on arrival.

But Lostock High’s assistant head teacher, Samantha Tsang, says making a school phone-free is “near impossible” without a legal ban and the resources to implement it.

“We do find that we are catching students trying to use their phones in social times, and we can’t see every corner of the school at all times”, Tsang says. “We need statutory guidance. If every school is doing the same thing, then it’s fair and we’d be more likely to get the buy-in from the parents and the families that we need.”

The school can’t afford pouches or lockers, and they have noticed some students hand in a second “burner phone” or a broken phone if caught.

Research by the University of the West of England showed that the common “off and in bags” approach does not prevent pupils from using phones during the school day, and parents underestimate the harmful content children can access.