London is a city with strict limits to building height and with protected views of certain buildings from particular locations (notably St Paul's). Permission to build skyscrapers in the centre of the city is granted on a case-by-case basis. For this reason, tall buildings in central London are notable landmarks.
Until the early 1960s buildings in London were restricted to 100 feet (30 metres) in height, although there were some exceptions to this rule. This restriction was put in place so as to keep every floor of a building in reach of the fire brigade's ladders. The lifting of the height restriction caused a sudden boom in the building of tall buildings during the 1960s.
Skyscrapers.com page on London (http://www.skyscrapers.com/re/en/wm/ci/100637)
Interim strategic planning guidance on tall buildings, strategic views and the skyline in London (http://www.london.gov.uk/approot/mayor/planning/docs/tall_buildings.pdf)