Image from w.a.s.t.e
Radiohead, one of the greenest bands on the planet, is flogging the clothes to go with the concert. Never mind wearing the tee-shirt, what about one better: a rain jacket made of "approximately 15 old bottles."
Given the weather across the land, this very cool and hip jacket, made of 100% certified recycled plastic PET bottles, will add a certain "je ne sais quoi" to your look, as well as being très environmental.
Images from w.a.s.t.e.
If you aren't into the logo look, but still want the tee-shirt, w.a.s.t.e., their on-line store, also does a white tee-shirt, with cap sleeves (very stylish and rock-chick) or regular ones. The shirts are are made from plastic bottles destined for landfill and organic cotton. "Pretty good for the environment as it happens" to quote their view.
They are also flogging the Sigg water bottle that is shaped from a single piece of pure aluminium, good for drinking under fake plastic trees.
Image from greenfingers.com
On the subject of green festivals and bad weather, here's the answer to your wet-feet problems: wellies made with no animal products. Sold by the Royal Horticultural Society, they are embellished with vegetables or roses, taken from vintage RHS prints. A perfect contrast to your jacket...maybe.