Somewhere near £1.50 I believe.
The problem is that beer duty unfairly hits local pubs, who have to pass on the price to their customers (i.e. A 1p rise at budget time can put 5p on in a pub), but the big chains and supermarkets can absorb it.
Hence, raising beer duty has no impact on cutting down binge drinking.
Edit for bonus info: http://www.thepublican.com/story.asp?storyCode=63085