Softening drug laws and banning school expulsions is the way to tackle the knife crime epidemic blighting London’s streets, according to the Liberal Democrats’ mayoral candidate.

Siobhan Benita accused London Mayor Sadiq Khan of doing “almost nothing” to tackle knife crime in the city, where more than 100 people, including more than 20 teenagers, have been killed this year as a result of blade attacks.

The former civil servant told the Lib Dem conference she would overhaul drug laws, ban schools from permanently excluding pupils, create safe zones for children to use after school hours and reopen police stations in the “heart of our communities”.

Mr Khan’s policing adviser, the former Metropolitan Police superintendent Leroy Logan, has left the Labour Party to work for Ms Benita.

Speaking at the conference in Bournemouth, Mr Logan said the mayor “doesn’t really understand” knife crime.

Ms Benita told delegates on Monday “something has gone horribly wrong” in London when it comes to knife attacks.

“Just this week, three people were fatally stabbed in Camden alone,” she said.

“Every stabbing is a national tragedy, with horrific grief for families, friends and communities.

“Sadiq Khan has wasted an entire mayoral term achieving almost nothing on this issue.”

The south Londoner, who is a child of an Indian immigrant mother and Cornish father, said police enforcement could not be the only answer to tackling the rise in violent murders.

She confirmed she would appoint a young mayor to advise City Hall and ensure “young people’s voices are heard every day”.

If elected mayor at the 2020 election, Ms Benita said no child in London will allowed to be permanently excluded from a mainstream school.

She also promised to create a “happy hour” when schools, churches, sports clubs could provide “safe spaces and enjoyable activities so not a single child is vulnerable to crime after school”.

The Lib Dem candidate previously told The Guardian she would support legalising marijuana to free up police time to target the drugs trade, a key factor in the rise in youth violence.

“The long-standing policy on drugs reform must begin in London,” Ms Benita told party members.

“I will end the failing war on drugs and instead wage war on the criminal gangs and drug lords.”

She predicted such measures could “begin to end the tragedy” of knife crime on the city’s streets.

Away from crime, Ms Benita – who previously stood as an independent in the 2012 mayoral race – said she would push for free movement to continue even if Brexit goes ahead, calling for EU citizenship to automatically qualify would-be migrants to live and work in London in any future Australian-style immigration points-based system.