The unlikely story goes that in the 1500s, the Dean of St Paul's was fishing in the river, bread and beer by his side, with the beer in a bottle for ease of transport. But mid-fish, he learnt that he was in danger of being arrested; so he fled, leaving his food where it lay.
Some time later he returned to London, and went down to the river again; where he was astonished to find his ale still resting in place. He opened the bottle to the unexpected sound of a huge bang, and the still more unexpected discovery that the beer was bubbly and drinkable still. And that, it's said, is how we discovered that you can bottle ale.