Thanks for your reply. I did manage to get one 10 years ago in Grove Park where there was a huge area of old overgrown allotments next to the railway line waiting to be developed. We started clearing it and digging - then I realised that the cluster of buildings running alongside the railway were sidings where the nuclear train transporting used plutonium rods for reprocessing at Sellafield stopped.

I'm afraid my heart went out of it then. I couldn't reconcile organic gardening with the possibility of radioactive contamination! Perhaps I was wrong. Should I investigate them again?