A few weeks ago, on my way to buy late night provisions from Tesco, the staff stopped me entering. On the floor lay a young black man in a pool of blood. Emergency services arrived, but whizzed past us, to tend to another young injured man around the corner. They had stabbed each other.

The visceral reality of such futile violence, now too often a feature of London life, hit home. Both young men survived. I was useless and stood in tears watching, but the shop employees and ambulance paramedics saved lives that night. Heroes.