Belgo Centraal is a Belgian (yes, Belgian) beer hall. It's located in Covent Garden, a short walk from the Covent Garden underground stop.
The "beat the clock" deal is the reason to come here. This is how it works: if you order one of three set meals (roast chicken, grilled sausages, or steamed mussles and fries, all including a glass of beer, wine, or soda) early in the evening (call Belgo for the exact hours) you pay the time - so if you order at 5:30, you pay five pounds, 30 p for your dinner.
The food is actually quite tasty (I can vouch for the mussles), and the place itself is an experience - the waiters wear brown monk's robes, and the decor is techno-warehouse.