Some drama shot on Super 16 was telecined to 14:9-15:9 letterbox (whilst still being edited in the 4:3 domain) before digital TV launched, so some shallow letterboxing was beginning to be seen outside of movies.
This includes 'Our Friends in the North' I think, which was shown as far back as early 1996 - presumably it's possible to remaster it in full widescreen but all DVD releases have been 4:3 with small black bars.
Annoyingly my one big TV drama I was in (BBC's 'Victoria and Albert' in 2001) was released on DVD in non-anamorphic widescreen, so letterboxed 16:9 in a 4:3 frame - the image quality's far less than I'd hope for a production so recent, but I should be happy at least it made it to DVD at all.
When I worked in playout (2005 or thereabouts), and 4:3 programmes had to be put on server as pillarboxed (12P16), the occasional transmission tape that showed up as 14:9 (14L12) was a bit vexing.
I think what we were meant to do was treat it as 4:3, but then widescreen viewers would see thick black bars at the sides and thin ones at the top and bottom.
What I usually did instead was ARC
it to 14P16, so widescreen viewers would get it full height but with narrow pillarboxes; and analogue viewers in a 14:9 letterbox as delivered - just with a bit of a loss of resolution from all the picture smushing.