Doctor Who: Battlefield (1989) written by Ben Aaronovitch and directed by Michael Kerrigan
The Seventh Doctor (Sylvester McCoy) receives a distress signal originating near the English village of Carbury in the early 1990s. Being a lad after an adventure, he shows up and discovers an archaeological dig near a fabled battlefield where King Arthur and Modred are supposed to have their final battle. Armored knights from another dimension show up and start fighting each other and the UNIT troops stationed nearby (they are guarding a nuclear missile that they brought in for no clear reason other than it becomes a plot device toward the end). With the Doctor's presence soon discovered, the UNIT people put in a call to retired Brigadier Lethbridge-Stewart. The Brigadier goes once more into the breach for his dear friend. In the mean time, evil witch queen Morgaine has shown up, mistaken the Doctor for Merlin, and is ready to summon the Destroy of Worlds to get what she wants. Mayhem ensues.
The plot is fairly interesting if a bit daft. The actors are all good, especially Jean Marsh as the well-written Morgaine, a villain with more depth than usual on the show. Her son Modred is a bit cartoony--his maniacal laughter goes on too long in some scenes. McCoy is good as the Doctor, able to swing from the comedically absurd to the dramatically heavy without looking silly. Weirdly, the sword fight scenes are much better than the gun battles. The alternate dimension knights have futuristic guns that use fairly inferior practical effects. Classic Doctor Who fans are used to some rubbish visual effects, I suppose. On the other hand, the makeup for the demonic Destroyer is quite impressive and the Lady in the Lake moment is great fun.
This set of four half-hour episodes is well worth watching.