"What's mild?" I hear you ask. It's probably the UK's greatest style of beer. Sweeter than bitter, less heavy than stout or porter.
If you can find a pub that does it (in the south and east of England, free houses are your best bet; in the midlands or north west you'll have more luck with regional brewers as it's more popular there)... ENJOY.
I've been an obsessive for mild ever since 1993, when I was having a pint with my dad in Oxford and a punter came into the bar and asked for mild and the barman said "I'm sorry, we don't serve it". Dad muttered "what sort of pub doesn't serve mild? This isn't a pub, it's a shithouse".
Nice one, dad.