London

London is the capital city of England and Great Britain, and the main setting in both series of Hellsing. London is the home of the British government, Royal family and many famous landmarks including the Houses of Parliament, Tower Bridge, The Tower of London, St Paul's Cathedral and Trafalgar Square, most of which are purposely destroyed by Millennium in their invasion of Britain.

Origionally a small settlement established by the Romans in 43 AD, London grew through the millenia to become capital of England, Great Britain and the British Empire which, judging by quotes made by Sir Integra Fairbrook Windgate Hellsing and the Major, may still exist in some form in the Hellsing universe, or may simply be formal or metaphoric references.

The headquarters of the Hellsing Organization appear to be situated in the countryside some distance from London's outskirts, which could explain why Walter C. Dornez predicted that it would take many hours for reinforcements to arrive during The Valentine Brothers' Ghoul Army's siege on Hellsing.

Appearances
The city of London appears frequently in the original anime series with the climactic battle in the last episode between Alucard and Incognito taking place in The Tower of London and St Paul's Cathedral.

In the Hellsing: Ultimate OVA and the manga, London is only featured properly towards the end, when is invaded and devastated by Millennium, with many of its famous landmarks destroyed by V2 rockets and a large amount of it's population killed by the bombardment of Millennium soldiers. Many of London's population was also transformed into Ghouls.

Millenium's Invasion
In the manga and 2nd anime, it is revealed that the upsurge in vampire attacks on British soil is the work of the sadistic Nazi organization Millennium, which has been hiding in South America since the end of the war, and has been building a battalion of vampire soldiers to reek revenge on those who defeated them, singling out Britain as their first (perhaps only) target, so as to destroy the Hellsing Organization and Alucard, both out of vengence for the part they played in destroying their earlier facility in Warsaw, and to remove them as a threat to their plans.