The Tallest building in the UK is in Canary Wharf, part of the London Docklands. One Canada Square, known as the Canary Wharf Tower, is 244 metres high and covered in stainless steel.
The O2 - Millenium Dome
The O2 in London is the largest dome in the world, covering over 180 acres; it is 320m in diameter and 50m high with support towers reaching 100m. It can accomodate Nelson's Column standing upright and the Eiffel Tower placed horizontally.
It was built on the Greenwich Meridian (0 degrees longitude) to commemorate the new millennium.