It was first shown on Monday evenings at around 5:15-5:20pm, beginning on 28 September 1970, in all ITV regions, apart from Thames (London) and Southern which broadcast the series the following Friday.

The main theme of the series is the way humankind uses and abuses science and technology, and tends to support the idea that the pursuit of scientific knowledge and advancement leads to the depersonalisation of individuals and the abandonment of moral principles.

Frank had served at the (now abandoned) naval research base in St Oswald during World War II, where he had suffered amnesia.

A local girl, Sarah, disappears through an invisible time barrier, witnessed by a local man, but nobody believes him when he tells the story in the pub where the Skinners are staying; but his story attracts a man called Charles Traynor (Denis Quilley), who arrives in the village and reveals that he was Skinner's commanding officer at the base during the war.

The staff of the Ice Box are conducting controlled experiments on human volunteers, including tests of a longevity drug called HA57.

A catalogue of failures has been plaguing the research effort, but Devereaux refuses to entertain the possibility that the base computer is making errors.

The staff, including Jean and Beth, each take a dose of an anti-freeze formula in the hope of surviving the cold until rescue arrives.

Determined to prevent the future of the Ice Box that they have witnessed, and curious as to what Traynor is afraid they might discover, they disobey him and once more enter the Time Barrier.

This time, however, she is a hippy Earth mother type who has rebelled against the technocracy that rules this future world, and lives in a primitive village with similar misfits.

Simon also encounters his future self – a technocrat known as Controller 2957 (David Graham), charged with implementing the Master Plan intended to reshape the Earth to the benefit of humankind.

His interference ruins the Earth's climate, causing global temperatures to soar and leading to an environmental collapse of devastating proportions.

Beth aids Liz and Simon in returning through the Time Barrier before heading for the safety of some caves with the misfits and 2957, who has seen the error of his ways, where there is water and they might stand a chance of survival.

Simon goes looking for Liz and tracks her to R1, a secret research establishment under Traynor's command, that is located at St. Oswald's and next to the Time Barrier.

Devereaux's experiments fail and the young people Simon and Liz encounter at R1 in 1965, they meet again in 1970 only now they are all very old men and women on the point of dying.

The Traynor clone is also a projection of the Time Barrier, charged with implementing Devereaux's vision of the future: the catastrophic Master Plan that will lead to the "Burn Up".

Timeslip was devised by ATV script editor Ruth Boswell, who developed the format and the outline of the first story with her husband James.

[5] Boswell was determined to come up with a show that was rooted more firmly in everyday life than Doctor Who, which at the time she felt had become progressively more outlandish.

The plot of the first serial, "The Wrong End of Time", was inspired by an – initially apocryphal (but according to some accounts confirmed after remaining a State Secret for more than 70 years)[7][8] – story of a German Expeditionary Force that landed in Britain to carry out a raid on an Isle of Wight radar station in 1940 (or 1943), during World War II.

[4] This view was echoed by an article in TV Zone magazine, which noted that Timeslip "was probably the general public's first introduction to what are now everyday scientific concepts, such as cloning and climate change".

[9] Although Boswell originally conceived Timeslip as a single-story six-part serial, the concept was soon expanded into a much longer series of 26 episodes.

[4] New Zealander Bruce Stewart, who had adapted various science fiction short stories for the anthology series Out of this World (1962) and Out of the Unknown (1965–71), was tasked with developing Boswell's outline into scripts.

The most notable location used was that of the Ministry Field where Liz and Simon discover the Time Barrier – this was in fact the Burnt Farm Army Camp near Goff's Oak, Hertfordshire.

For her audition as Liz, she dressed in trousers and sported a pigtail to emphasise the tomboy nature of the character – an image that stuck for the duration of the series.

David Graham (Controller 2957/Simon Randall) was a regular voice artist in the Gerry Anderson Century 21 Supermarionation series.

Reviewing the first episode in The Stage, John Lawrence said, "I always feel wary of programmes that are announced as "science fiction" since too often the description is applied to something that uses wild and improbable events to jump gaps in otherwise badly conceived stories... Judging by the first episode of ATV's new series, Timeslip, by Bruce Stewart, however, this programme looks like it might prove to be a welcome exception.

[16] Later, in 2005, SFX went on to poll its readers for their list of the top 50 British telefantasy shows and Timeslip was voted into twenty-eighth position on the list, the magazine describing it as "surprisingly intelligent and thoughtful SF with some ambitious ideas" and a series that "dared to be more adventurous with its science fiction than most so-called grown-up SF shows".

An exception was episodes 23 and 24, which were recorded in black and white due to the so-called colour strike, an industrial action by technicians that affected many ITV programmes at this time.

[21] The complete series – including the surviving colour episode – was released in a four disc region 2 DVD boxset by Carlton in 2004.

It features interviews with many of the surviving cast members, including Cheryl Burfield, Spencer Banks, David Graham, Ian Fairbairn and Iris Russell as well as creator Ruth Boswell, writers Bruce Stewart and Victor Pemberton and director Ron Francis.

A comic strip, which depicted several new adventures for Liz and Simon, appeared concurrently with the broadcast of the series in Look-In, a juvenile spin-off of the listings magazine TV Times.