The first companions one of these posts didn't generate anything like the same conversation as the Doctors ones, so if there's less interest this will likely be the last one. As may become clear, I'm a huge Anneke Wills fan.
Anneke Wills
Some People (bits)
Strange Report (1969-1970)
* Besides Doctor Who, this appears to be what she's best known/remembered for. General opinion seems to be positive, although personally I can't get past the vibe of astonishing inauthenticity.
The Strange World of Gurney Slade (1960)
* Genuinely bizarre ITV series, but a personal favourite of mine. All episodes on YouTube.
The Pleasure Girls (1965)
* Nowhere near as seedy as it sounds, honest, this is actually a really enjoyable film full of gorgeous people, which may or may not include Mark Eden (Marco Polo to us lot). It's good, but unfortunately the "swinging" part of the 60s is far more interesting than the actual story, and the film seems to know it.
Frazer Hines
Emmerdale (1972-1994)
* In his native, non-Scottish accent.
Lost at Christmas (2020)
* Playing Sylvester McCoy's husband.
Deborah Watling
Take Me High (1973, bits)
* The "Brumburger Duet" number (tis a Cliff Richard vehicle after all) is one of those all-time awful musical tunes.
Caroline John
Love Actually (2003)
* Apparently. Although I didn't spot her at the time, she is in it, although pretty unrecognisable it has to be said.
Katy Manning
Armchair Theatre (1973 episode, bits)
* Now this one genuinely is interesting. In a 1973 episode of this Katy played one of television's (worldwide, apparently, although citation needed methinks) first lesbians. It was based on a play called The Golden Road, and a clip on YouTube is currently the only way to see it. It isn't missing: it exists in the archive, but has strangely never been released commercially alongside the majority of the existing episodes.
Katy was also in an episode of "hard-hitting" BBC detective series Target. I had no luck finding the episode, so haven't included it here, but have seen others before. Don't be put off by the series' creators being Bob Baker and Dave Martin (two of Doctor Who's shakiest writers, and responsible for K-9): it's surprisingly sturdy, and has superb opening titles.
Elisabeth Sladen
* Turns out, there's a channel on YouTube for just this, which, while not comprehensive, is a fine gallery of her brilliance. I mention the clips from "Lost I'm France" particularly because they also star John Simm.