London is the capital and largest city of England and the United Kingdom. The city stands on the River Thames in the south-east of England, at the head of its 50-mile (80 km) estuary leading to the North Sea. The City of London, London's ancient core and financial centre − an area of just 1.12 square miles (2.9 km2) and colloquially known as the Square Mile − retains boundaries that closely follow its medieval limits.

Mumbai, formerly known as Bombay, the official name until 1995) is the capital city of the Indian state of Maharashtra. According to the United Nations, as of 2018, Mumbai is the second-most populous city in the country after Delhi and the seventh-most populous city in the world with a population of roughly 20 million.