ITV (Independent Television)
(launched in 1955)
IMDb; official website; TV Tropes; Wikipedia

This is a British network that I've never seen directly, but I've seen some of its shows on various American channels (mostly PBS or CBC).

The Prisoner (9/29/1967 - 2/1/1968)
The Muppet Show (9/5/1976 - 5/23/1981; aired in syndication in the US)
The Adventures of Sherlock Holmes (4/24/1984 - 4/11/1994; I've seen a bit of this, but I don't remember it well)
The Worst Witch (11/1/1986; TV movie; aired on HBO in the US)
Escape from Sobibor (5/10/1987; aired on CBS in the US)
Poirot (1/8/1989 - 11/13/2013)
Capital City (9/26/1989 - 12/20/1990)
Mr. Bean (1/1/1990 - 12/15/1995)
The Piglet Files (9/7/1990 - 5/10/1992)
Cadfael (5/29/1994 - 12/28/1998)
Boudica (9/28/2003; TV movie)
Mansfield Park (3/18/2007; TV movie)
Demons (1/3/2009 - 2/7/2009)
Houdini & Doyle (3/13/2016 - 5/12/2016; aired on FOX in the US and Global in Canada)

stuff I want to see
The Avengers
Broadchurch
Children of the Stones
Danger Man
The Darling Buds of May
Downton Abbey
Emma (TV movie)
Jeeves and Wooster
Prime Suspect
Reilly, Ace of Spies (miniseries)
Robin of Sherwood
Space: 1999
The Tomorrow People
Touching Evil
UFO
Upstairs, Downstairs
Victoria