Yes, pretty much. Just think of very small shrimp, covered with thousand island dressing, in between two thin slices of bread. Quite nice too, they're generally the dearer option of pre-made sandwiches in supermarkets, and often served with corporate catering spreads.
The reference is from a famous (within English soccer) article about Roy Keane (one of the manc's better, although nastiest players). When the gloryboys were filling Old Trafford a few years ago, they'd leave the game early if the side was losing, and start having a go at the players over the smallest thing. Keane got pissed off with it and had a go back. He was basically saying they weren't proper fans and didn't understand the games, or something like that. It created a stir at the time, and "prawn sandwich brigade" has been used as a derogatory term for certain "supporters".
Glasgow Celtic, also rather good with silverware, because they're basically the other team is Scotland. One of the Glasgow sides generally wins. They have:
League: 42
Cup: 34
League cup: 14
European cup (now called Champions League): 1
Not bad eh? There was talk of the two Glasgow teams joining the English league a few years ago. After all, their tin-pot league is worthless, and the English league already contains some Welsh clubs. It never happened, not sure why. Probably scotty FA politics and the clubs being somewhat unlikely to qualify for European competitions, which is where clubs earn big money with TV revenue.