So far as we know, no-one has yet discovered the secret of time travel. But that hasn't prevented TV and movie writers coming up with innumerable stories that involve travelling backwards and forward through the centuries.

The most famous time traveller - at least for British TV viewers - is surely Doctor Who. the Doctor first appeared on TV screens in the guise of a bumbling but razor-sharp old gentleman travelling around the galaxy, and through time, in the compnay of his granddaughter Susan. By the end of 1964 the Doctor had introduced us to the Daleks, surely the scariest pepperpots ever to roam the universe on wheels attempting to take over other people's planets.

British viewers who were young in the 1970s will also remember the series Timeslip, in which two schoolchildren climb through a hole in a fence and find themselves transported back to the Second World War, then forward to an antarctic research centre twenty years in the future.

On a less serious note, at around the same time British audiences were treated to the adventures of Catweazle, an 11th-century magician who is transported to the 20th century as he tries to escape capture by Norman soldiers. He is perpetually baffled by modern inventions such as 'electrickery' and the 'telling bone'.

Cinema goers were exposed to an orgy of time travel in the 1980s. In 1984, it was The Philadelphia Experiment, in which a battleship from 1943 is transported forward in time by 40 years. Also that year Arnold Schwarzenegger made his debut as the homicidal android in The Terminator. In 1985, Michael J. Fox travelled back to the 1950s in a time machine constructed by his friend Doc Brown out of a De Lorean car. He accidentally prevents his parents from meeting, thereby ensuring he won't be born, and then has to try and put things right. Two sequels followed. Meanwhile, in 1986, Kathleen Turner starred in the film Peggy Sue Got Married, as a woman who - surprise, surprise - travels back to the 1950s and meets her parents.

TV soon caught up with the arrival of Quantum Leap in 1989. In this show the hapless scientist Sam Beckett is forced to travel throughout his own lifespan, leaping into the bodies of a variety of different people at critical moments so that he can sort out their problems. At one point he even 'leaps' into his own body as a teenager.

In November 1993, the BBC broadcast the first episode in a series called Goodnight Sweetheart, in which Nicholas Lyndhurst plays Gary Sparrow, a TV repairman who walks down an east London alley to find himself timewarped back into the Blitz. He ends up leading a double life, half in the 1940s and half in the 1990s, with a girlfriend in each time zone.