I had these in London a bunch of times when I couldn't resist the fish & chips at the pubs. I describe them as peas mushed up with lots of salty goodness; here's the actual, Wikipedia definition. Either way, I love them, and have never come across them in the States before. I'm sure there are tons of places that serve them, but for some reason I've never seen any.
Here they are in all their glory from my 2006 trip to Brighton, England.Here's the menu for The Landsdowne.