She was the respected allotment committee secretary, he was an ambitious fellow plot holder: why did he kill her?

In a corner of London, close to the busy Edgware Road, there is a secret garden. Tucked away on a residential street, the gate has the words “Colindale Gardens and Allotments Association” messily painted on a white plank tied to the chain-link fencing. Beyond the gate is a broad expanse of grass and earth, of greenhouses, sheds, canes and polytunnels. You can hear the occasional rumble of a train, and in the distance you can see cranes constructing blocks of flats to house the next generation of gardenless Londoners. But the space here is so peaceful, so lush and full of birdsong, that you almost forget where you are.

The Colindale allotments are home to 90 long plots, mostly 20 metres by eight, arranged along two parallel grass avenues. The rules say sheds can be put up only on the end farthest from the path, giving the space the look of a miniature suburban neighbourhood, with plots in front of sheds instead of lawns in front of houses. A plot costs £85 a year. There are currently 60 people on the waiting list.