In the British Parliament building, the Palace of Westminster, there are two parliamentary houses. The House of Commons is in the northern part of the building, in which ministers sit on green leather benches. In the southern part of the building is the House of Lords; here, incumbents sit on red leather benches.
Spanning the river Thames, which flows past the Palace, there are two bridges: Westminster Bridge to the north, coloured green, and Lambeth Bridge to the south, coloured red.
(via London Leben.)