The 200

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

History
When the transit through the wormhole took place, the 200 had eight passengers, including the Doctor, the fugitive Christina de Souza 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, also visiting San Helios, though through conventional means, mistook the 200 for a weapon, though the Doctor disabused them of this notion. The bus was badly damaged and was stuck in the sand but the Doctor used an alien device to fly it back back through the wormhole, the bus driver having died, back to London, pursued all the while by the ravenous Swarm. He had fitted the bus with anti-gravity clamps from the Tritovore ship to enable it to fly. Back on Earth the Lady de Souza took opportunity of a distraction, and secretly, the Doctor's help, to steal the bus and escape in it, flying away. (DW: Planet of the Dead)

Behind the scenes

 * The number 200 commemorated the two hundredth Doctor Who story aired on television, namely Planet of the Dead itself. The real bus route 200 does not terminate at Victoria, and instead runs from Raynes Park to Mitcham via Wimbledon.
 * The damage done to the bus when going through the wormhole in the story was not actually intentional - the bus was damaged during transit due to 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.