I try not to read the free london papers too often, because they're so full of brain-rotting drivel, however glad to be perusing one on Friday last, as I came across an article about organic vineyards, to be planted in central London!
The wholefoods company Alara, has their hq near kings cross and is planning to plant some vines on some old railway ground there.
Even better, their inviting people along to help planting, and providing a free lunch to volunteers! see http://alara.co.uk/193,l2.html . I can't find anywhere to sign up so I assume you just turn up. I have put it in my diary and just hope it is as beautifully spring-like a day as today!