I was rather surprised to see a blogger tweet that it's National Beer Day today (7 April). I thought it was later in the year, so I googled it, and I was right: National Beer Day in the UK is on 15 June.
Britain's beer day is on 15 June because on that date in 1215, the Magna Carta was sealed. Article 35 states: Let there be throughout our kingdom a single measure for wine and a single measure for ale and a single measure for corn, namely the London quarter. That reads to me as an early example of weights and measures legislation.
Digging a bit further, I found that the Icelandic National Beer Day is on 1 March, marking the end of a 74 year prohibition on beer that began in 1915 and ended on 1 March 1989. Curiously, the ban on wine was lifted in 1921, and that on spirits in 1935. It was felt that beer, being weaker and cheaper, would lead to widespread depravity; this measure was therefore an early example of beer price rationing inspired by moral panic. I'm almost impressed by the prescience of the Icelandic killjoys!
These beer days are mainly for fun, I suppose, plus a bit of publicity for those making and selling beer, but last year the UK beer day completely passed me by. I'll try to do better this year.