A Brent headteacher fears pupils could take knives into school if there was no strict policies on uniforms.

Katharine Birbalsingh, who leads Michaela Community School in Wembley, said giving students small matters to ‘rebel’ against – such as rules on school uniforms – was important.

She told radio station LBC it was crucial youngsters, when they do rebel, choose something unimportant rather than more dangerous issues such as keeping a knife with them at school.

Ms Birbalsingh said: “The reason we have rules that can sometimes seem a bit pedantic to the public is so the children don’t misbehave in big ways.

“What I mean by that is, when you have a uniform you can say ‘ties to the top, shirts tucked in’.

“And, when they want to rebel, they pull their shirts out and they make their ties fat and short.

“That’s what children do – they rebel. And you want them to be able to.

“But you want them to do it with things that don’t really matter because, at the end of the day, whether their tie is long or short isn’t really going to make a big difference.

“Depending on your intake and where you are – if you’re in the inner-city for instance – if you don’t have uniforms, then they rebel by bringing in knives.

“Now I know that seems a bit extreme but, I promise you, if you don’t have rules about the little things, the big things become an increasing problem.”

Ms Birbalsingh, who chairs the Department for Education’s social mobility commission, acknowledged different schools adopted different approaches.

She said teachers should be able to make whatever decisions they see fit and which are, in their view, right for their student population.

Michaela, a free school set up in 2014, has been described as one of the strictest schools in Britain.

On its website, it notes there is a “belief that the teacher is the authority in the classroom” and “without excellent discipline, learning cannot take place”.

Its uniform policy states that shoes should be polished at least once a week and children should wear a clean shirt each day.

Ms Birbalsingh and Michaela Community School have been contacted for comment.