For the first time ever, more beer (51%) is sold in shops than in pubs. The British Beer and Pub Association puts most of the blame on the beer duty escalator, pointing out that, despite recent cuts, duty is 54% higher than it was in 2000, and is 14 times the German rate. In 1980, 87.7% of UK beer sales were in pubs, a figure that has declined ever since.
While I don't disagree with this point, there is another reason that I haven't seen mentioned: in 1980, supermarkets didn't sell alcohol alongside the baked beans. I well recall the massive fuss when a supermarket in Southport applied for an off-sales licence; I cannot remember the year, but it was well after 1980. The licence was granted but with restrictions that seem odd today, including that it had to be in an entirely separate room with its own till, and that alcohol could not be paid for at any other till in the shop. I'm not quite sure, but I think that there might even have been a stipulation that any alcohol bought in the off licence section could not be carried unwrapped in the rest of the supermarket. As we all know, drink is now stocked in the normal aisles and paid for like everything else.
The difference between having a separate shop within a shop and the current situation is that it allows for impulse purchases; it also removes the implication that alcohol sales are something slightly shameful to be hidden away. Buying alcohol with your everyday groceries has now become completely normal. In recent years the number of convenience stores with an off-sales licence, many run by the big supermarket chains, has multiplied, resulting in a further increase in the number shops that sell alcohol. Ironically, quite a few of these are in former pubs.
It's also worth noting that making alcohol so much easier to buy has one entirely foreseeable consequence which - oddly enough - no one seemed to foresee: that it would also make under-age purchases easier. In this way do we unwittingly create new causes for moral panic.
* My own list of suggestions for the decline is here.