I found some at the bargain price of £30 when I looked. Try www.wine-searcher.com. (Almost as cheap as the case of 1980 (not such a good year) I bought whilst an undergraduate. There's a bottle still left somewhere in my cellar, I think.)
Pinky's also sell George Gardet champagne at 10.99. That's extremely good value fizz at that price.
I'm lucky enough to have bought a case of Warre '77 in (I think) the late 1980s. Drank the first bottle this Xmas and it was excellent. Though not sure if it has been an especially good financial investment: I think I paid a bit over £10 per bottle. Still nice to anticipate the other 11 though! And since the topic moved on to Champagne, do you know the Champagne Club at the Great Eastern? A great evening every couple of months or so tasting a few wines from a particular house.