Wikipedia
P.R.O.B.E. is a series of videos mostly written by Mark Gatiss and produced by BBV Productions. It predates Torchwood as the first ongoing spin-off of the Doctor Who universe.
The series features Caroline John as Liz Shaw, working for the Preternatural Research Bureau. Many former Doctor Who actors, including former Doctors Jon Pertwee, Peter Davison, Colin Baker and Sylvester McCoy, appear in the series playing different roles. (Due to licensing restrictions, no overt reference to The Doctor is permitted.) Doctor Who alumna Louise Jameson co-stars with Caroline John in all four films, as Patricia Haggard.
Originally released on VHS, the series is not widely available on video. When an interviewer commented to series author Mark Gatiss that he had never seen the series, Gatiss replied "No, and you never will. One, they're not available. And two, I forbid it. Christ, for all I knew, they were the only things I would ever get to make. And I learned a frightening amount from working on them." All four films were released on DVD on 3 March 2012 exclusive to Galaxy 4 shop with a 12 rating.
A fifth film written and directed by Bill Baggs was released 20 April 2015 with Hazel Burrows taking over as Liz Shaw.