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
London appears frequently in series 1 with the climactic battle between Alucard and Incognito taking place in The Tower of London and St Paul's Cathedral.

In series 2 and the manga, London only features properly towards the end, when is invaded and devistated by Millenium, with many of it's most famous landmarks destroyed by V2 rockets, and a large amount of it's population killed by the bombardment and Millenium soldiers, with many transforming 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.