London - city, capital of the United Kingdom and the centre of the Commonwealth. It lies astride the River Thames in southeastern England, 50 miles (80 km) from the river's estuary on the North Sea. The city was once the industrial, commercial, and political hub of a wealthy and extensive empire; it continues to be the United Kingdom's main centre of population, commerce, and culture. A brief treatment of London follows. For full treatment (including a map), see London. The chalk ba...