The 200 was a modified double-decker bus taken as Lady Cristina de Suza's spaceship in the episode planet of the dead.
By the start of the series of books, Cristina had repaired the heavily damaged bodywork and fully replaced the engine to allow the wheels to work.She had also strengthened it and added air systems for space travel.
In the first 200 book, she received plans to use the antigravity plates in reverse to warp space enough to create a time travelling wormhole around the craft, it later transpired that she gave these plans to herself due to a temporal paradox.
Also later added was a teleport system to allow her to travell across space in an instant.Both the time travell and the teleport systems were controlled from a stolen laptop mounted in the driver's seat.
Although the lower deck remained largely unchanged save for the addition of the laptop and a large air recirculater salvaged from a crashed plane,the upper deck was adapted into a living area by adding a bed and a cooking area.