Whilst everyone says 'What about us who drink responsibly?', well generally we drink less, so the price is lower anyway, And 40p a unit isn't that bad - can you get a shot of vodka anywhere for 40p in a pub? No. In a 70cl bottle of vodka, there's 30 shots, which, multiplied by 40p = £12. Which is pretty much what you pay for a 70 cl bottle of Smirnoff anyway. If you do drink responsibly, than a 70cl bottle would last you a while anyway.
So it's a great idea.