Doctor Who
694 serial episodes (1963-89) 30m & 60m

Worth every bit of its lofty cult status, the Doctor is a Time Lord who periodically regenerates every time a new actor takes over the role - the most popular being Tom Baker (1974-81). Time and space are explored in the TARDIS, which is much more spacious inside than its outward appearance would suggest. Well scripted. New series from the 2000s listed separately.

Planet of the Apes
14 episodes (1974) 60m

After a host of successful feature films, a series seemed somewhat excessive - even a little nonsensical. Roddy McDowell reprised his role as the compassionate ape who befriends two time-tripping astronauts in a primate-dominated future. The group stayed on the run for 14 episodes until the series was mercifully canned.

Sapphire and Steel
34 serial episodes (1979-82) 30m

Completely bizarre, absolutely no scientific foundation and immensely enjoyable. The title characters (played by Joanna Lumley and David McCallum) are dimension-hopping temporal agents whose job it is to plug leaks between the past, present and future - which is apparently what causes most supernatural phenomena.

Quantum Leap
95 episodes (1989-94) 60m*

Sam Beckett (Scott Bakula) wanders through various near-past locations facing an array of moral dilemmas while occupying other people's bodies. Somewhat confusingly, Beckett appears as himself to the camera, but the characters around him see only the body he occupies & can't see his hologram sidekick at all. Good-natured fun.

Sliders
88 episodes (1995-2000) 60m

Young genius Quinn Mallory inadvertently opens a time portal, which for the rest of the series takes him and his three companions to a host of parallel Earths. Production costs were kept to manageable levels by sticking to contemporary scenarios, thus avoiding the necessity for too many elaborate historical or futuristic sets.

7 Days
66 episodes (1998-2001) 60m

The adventures of a "chrononaut" Frank Parker - a government agent who is frequently sent up to seven days back in time to fix things when they have gone haywire. Parker travels courtesy of an invention that was created using alien technology from the Roswell crash. Well-made series with a strong cult following, lasting just long enough to score some reruns.

Doctor Who
In production (2005-present) 45m

The new Doctor Who has managed to bring the show into the modern world without ever losing its sense of historical identity. Now featuring mainly self-contained episodes, star Christopher Eccleston used up an entire regeneration when he quit after only one series, ably replaced by David Tennant. Quality revival well-received by the fans.

Terminator: The Sarah Connor Chronicles
In production (2008-present) 60m

Based on the Terminator franchise, this series revolves around the title character's efforts to protect her historically significant son John from an army of SkyNet cyborgs determined to knock him off. She gets some help from a hot young Terminator babe played by Summer Glau, who takes them time tripping in an attempt to head off Judgement Day. Surprisingly satisfying series.