With thanks to Peter Darrington

Image © BBC

The TARDIS is the time machine used by the title character of the BBC television programme Doctor Who, the name TARDIS being an acronym for Time And Relative Dimensions In Space. As well as being able to travel to any point in time and space, the TARDIS has a chameleon circuit, which enables it to alter its external shape so as to blend in inconspicuously with its surroundings. When the Doctor visited Earth in late 1963 his TARDIS materalised in the shape of a police box. The chameleon circuit then promptly failed, leaving the TARDIS stuck as a police box.

One of the more fascinating aspects of the TARDIS is that its exterior and interior do not exist in the same dimension. The practical upshot of this is that its interior is dimensionally transcendental; in other words, it's bigger on the inside than on the outside.

The decision by the production team for the TARDIS to be permanently in the shape of a police box was probably made for budgetary reasons, as otherwise a new exterior would have been required for each story.

Amazing as the TARDIS' chameleon circuit is, the police box featured in Dr Who actually differed from the genuine article in various ways, despite (or maybe because of) the number of prop police boxes built during the programme's production. Perhaps the most consistent and obvious difference is that the TARDIS' door opened inwards, whereas that of a genuine police box opened outwards.

The police box used in the pilot episode of Dr Who was one that the BBC already had in their Stores, as it had been constructed in the late 1950's for the series Dixon Of Dock Green. This police box, however, proved difficult to transport in the lift at the Lime Grove Studios, and so when the go-ahead was given to produce Dr Who another police box was built. The new box was almost 8 inches shorter than the pilot episode one, this being achieved by making the plinth two inches high instead of four, and making the roof area lower too. It was constructed from wood, and painted with artex in the paint so as to give an appearance of concrete. This box was not collapsible, and was used from 1963 to 1975.

Meanwhile, the pilot episode box was stored at Ealing Studios for many years. It was lent to Kevin Davis for the documentary "30 Years In The TARDIS", before being returned to the BBC for storage. It was eventually bought by The Sun newspaper in an auction for £3,000, who used it in a World Cup publicity campaign. This campaign consisted of photographing Jeff Hurst in the doorway of the police box at Wembley, with a headline about going back in time to 1966, when England won the World Cup. After being stored by The Sun in a warehouse in Wapping for a couple of years, it was acquired by an employee of Tom Baker's management company.

During the filming of the story The Seeds Of Doom in 1975, the roof of the TARDIS prop fell in on actress Elisabeth Sladen, who played companion Sarah-Jane Smith. Another police box was commissioned, this one being collapsible for the ease of transport. This new prop was used from The Masque Of Mandragora (1976) to Shada (1980). It then cropped up again in Logopolis (1981), for which it was given new glass and a new roof. It was also used in Castrovalva (1982) as the "crashed" TARDIS, as the fibre glass prop used for location work was not felt to be robust enough to be tipped on its side and have actors clamber in and out of. It also appeared in The Black Orchid (1982) for reasons unknown, before being sold in auction. It now resides in a private transport museum in Birmingham (UK).

In 1980, producer John Nathan-Turner commissioned two new TARDIS props, both made from fibre glass. These were more mobile than the wooden props, which were heavy and difficult to transport for location work. Of these two new props, one was collapsible and the other wasn't. The BBC still has the non-collapsible prop, and it was most recently seen in the Comic Relief sketch and in the Doctor Who Evening in November 1999. The other prop was sold in auction shortly after Dr Who was cancelled, and is now in the hands of Andrew Beech. It is featured on stage at every Panopticon convention.

Separate and specially-commissioned TARDIS props were built for the Peter Cushing films of 1965 and 1966, and also for the Paul McGann television movie of 1996.

Several scale model police boxes were presumably made for special effects work over the years that Dr Who was in production.

On 26th March 2005, Doctor Who made a spectacular return to the small screen, with Christopher Eccleston as the Doctor. This of course meant that yet another TARDIS prop was constructed.

Finally, the word "TARDIS" became an official word in the English language with an entry in the 2002 edition of the Oxford English Dictionary.