Education secretary Damian Hinds has defended the school exclusions system and suggested that truancy could be a better indicator for knife crime.

He said a "much bigger concern" than expulsions are those who are "persistently absent", which includes pupils who skip school or are long-term sick.

Earlier this month London mayor Sadiq Khan and seven police and crime commissioners wrote to the prime minister warning that a "broken" exclusion system was contributing to the issue.

But Mr Hinds, writing in today's Daily Telegraph, said the "reality is more complex", with only about 3 per cent of knife attacks perpetrated by someone excluded in the previous year.

Quick read: Sadiq Khan: 'I’m not blaming schools for knife crime rise'

One study suggested four-fifths of young knife offenders were persistently absent in one of the five years leading up to the offence, he added.

"They may be disillusioned, disengaged or ultimately coming from a home where going to school is not the top of the priority list," Mr Hinds said.

"It is these children, children from homes where parents have experienced one or more of the trio of mental health problems, domestic violence and substance abuse that are most at risk of harm or criminal exploitation."

Permanent exclusions in England increased by 56 per cent between 2013-14 and 2016-17.

Ofsted chief inspector Amanda Spielman has said the issues leading up to a pupil's exclusion, rather than the exclusion itself, were more likely to explain violence.

Mr Khan and the police leaders earlier this month wrote to Theresa May, saying: "It cannot be right that so many of those who have committed offences have been excluded from school or were outside of mainstream education."