Sainsburys do Celebration Ale each winter, a 6% stout from Black Sheep in Masham. That and Lee's Manchester Star Ale are always on my shopping list there.
Re M&S beers, I managed to pick up 40 bottles of the Cornish 6 Malt Stout (Mena Dhu rebadged) and it worked out at under ã1 a 500ml...