The 200

The 200 was a London double-decker bus transported by a wormhole to the planet San Helios.

History
When the transit through the wormhole took place, the 200 had eight occupants, including the Tenth Doctor, the fugitive Christina de Souza (evaded the police by hopping on a the 200 bus) and its driver. It was running an evening service bound for London Victoria station via Vauxhall, Oval and Brixton. The bus's number plate was "W974 GHM".

A small party of Tritivores who had crashed on San Helios mistook the 200 for a weapon. The bus was badly damaged and stuck in the sand, however, so the Doctor fitted it with anti-gravity clamps from the Tritovore ship to fly it through the wormhole, back to London. However, the 200 was pursued by the ravenous Stingrays, which where shot down by soldiers. Back on Earth, Lady de Souza took opportunity of a distraction and the Doctor's secret help to steal the bus and escape in it, flying away. (DW: Planet of the Dead)

Later, during his eleventh incarnation, the Doctor said that the Timeship had created a rift large enough to drive a double-decker bus through, and mentioned that he had actually done that before. (NSA: Paradox Lost)

Behind the scenes

 * The number 200 commemorated the two hundredth Doctor Who story aired on television, Planet of the Dead. The real bus route 200 does not terminate at Victoria. It runs from Raynes Park to Mitcham via Wimbledon.
 * The damage done to the bus when going through the wormhole in the story was not intentional - the bus was damaged during transit by an accident involving a crane in Turkey. However, this gave the impression of damage and showed how dangerous the wormhole actually was, so instead of repairing the bus, it was touched up to look burned as well as gashed.