Greater London

The Great City of London was lost when the Tower of London fell. The rising sea levels swelled the banks of the tidal river Thames. The river rose to levels not seen in millenia. With the Thames overflowing its banks the city was quickly inundated and submerged. Those who lived on the outskirts of the city fled to higher ground in hopes of escaping the flood.

Demographics

Age structure and median age

The average percentage are as follows: Children younger than 14, 19.6%. 15–24, 10.9% 25–44, 35.8% 45–64, 22.2% 65 and over, 11.6%
The median age of London was 36.5.

Ethnic groups

Ethnic groups in London
According to the Office for National Statistics, 59.8 per cent of the inhabitants of London were White, 44.9% White British, 2.2% White Irish, 0.1% gypsy/Irish traveller and 12.1% classified as Other White. Londoners of Asian and mixed-Asian descent made up 20.9%.
Those of Black and mixed-Black descent make up 15.6% of London's population.

Religion

Of the religious groupings Christians made up 48.4%, those who claimed no religion made up 20.7%, Muslims made up 12.4%. Those who refused to responsd made up 8.5%, those who claimed to be Hindus made up 5.0%, while Jews were only 1.8%, Sikhs 1.5%, Buddhists 1.0%, and other primarily pagan styled reigions were a platry 0.6%.

Accents

Cockney is spoken primarily by the working-class and lower-middle class. It is attributed to the East End.
Estuary English, an intermediate accent between Cockney and Received Pronunciation is widely spoken by people of all classes in London. It has been associated with the River Thames estuary.
Received Pronunciation the accent traditionally regarded as the standard for British English.

Government

The government of London is two tiered, The General Legislative Assembly (GLA) and Local Administration. The GLA is a city wide structure with an elected mayor and the London Assembly. The Local Administration is made up of thirty-three districts.

I gathered a good portion of my information from the London Wikipedia article

RUINED SETTLEMENT
June 1, 2174

Founding Date

47 AD

Alternative Name(s)

London town, Londinium

Type

Capital

Population

At the time of its sinking under the ocean 12,532,344

Location under

England

Owner/Ruler

King/Queen of England

Ruling/Owning Rank

Their Royal Majesty

Owning Organization

United Kingdom