It was one of the first regular programmes in the line-up of the channel, and the title referred to its production and transmission being in the higher-definition 625-line format, which only BBC2 used at the time.

[1] Some of the best-known productions made for the series include a new version of Nigel Kneale's 1954 adaptation of George Orwell's Nineteen Eighty-Four (1965); the four-part Talking to a Stranger by John Hopkins (1966) which told the same story from four different viewpoints, and features Judi Dench; and 1968's science-fiction allegory The Year of the Sex Olympics, again by Kneale.

IMDb and the BBC Genome database (of Radio Times listings) have been used as a check, and occasionally as the main source.

The information about the episodes survival status in the last column is taken from the TV Archive website and The Kaleidoscope BBC Television Drama Research Guide, 1936–2011,[4] and are correct as of 9 January 2024.

[5] Legend: Se = Season; Ep = Episode; AS/A = Archive status/Availability Abbreviations: tr =Telerecording; seq = sequence(s); VT = video tape All known copies are black & white, except where stated otherwise.