The stabbing deaths of two teenagers in the course of one weekend earlier this month have reignited the debate about knife-crime in the UK. In the year ending March 2018, fatal stabbings in England and Wales reached their highest level since records began more than 70 years ago, with almost 40% of all knife offences occurring in London. But an innovative project in London is trying to convert the destructive into something constructive - by taking seized and surrendered knives off London's streets and melting them down to make outdoor fitness parks.