Haircut and uniform violations are being punished by schools as severely as drug and weapons under “zero tolerance” policies, MPs have warned.

Pupils are being “punished needlessly” for minor offences under strict behaviour codes and this is fuelling the escalating number of expulsions across England, according to a new report published by the education select committee.

“Zero tolerance” behaviour policies have become a popular among headteachers as they seek to instill discipline and improve results.

But such policies have been criticised by MPs who say they are leading to more students being temporarily or permanently excluded from school.

“We have heard that there is an increase in zero-tolerance behaviour policies, contributing to the rise in exclusions and increase in pupils attending alternative provision,” the report said.

“While it would be reasonable of schools to take a zero-tolerance approach to drugs or weapons, a school culture which is intolerant of minor infractions of school policies on haircuts or uniform will create an environment where pupils are punished needlessly where there should be flexibility and a degree of discretion."