The union of head teachers has backed pupil plans to walk of their lessons in a "strike" to protest climate change.

The mass strike, organised by teenagers and called UK Youth Strike For Climate, is aiming for thousands of students to put down their work and leave their classes this Friday between 11am and 2pm.

Pupils from schools in 27 towns and cities across the UK including Cardiff, Brighton, Exeter and Glasgow have vowed to leave their lessons - and their decision has been backed by headteachers.

The National Association of Head Teachers said in a statement: "When you get older pupils making an informed decision, that kind of thing needs to be applauded.

"Society makes leaps forward when people are prepared to take action.

"Schools encourage students to develop a wider understanding of the world around them, a day of activity like this could be an important and valuable life experience."

However, others have referred to it as "playing truant", adding that pupils will take any chance to miss school.

Former primary school teacher and Conservative MP William Wragg told the Sunday Express: "I would not encourage a walk out, it's far more fruitful to learn about climate change in school."

Toby Young, former director of the New Schools Network, said: "Calling this a strike is ridiculous. What are they going to do? Down pencils? This is just truanting."