I saw this on WTTG Channel 5 in Washington early Saturday mornings in the early '80s. Then it resurfaced on A&E about ten years later. Yes, that was the same actor who played Ford Prefect on TV playing Prince John. Then it disappeared again. The other poster was absolutely right. WHEN WILL WE SEE THIS ON DVD??????!!!!!!! (I'm not allowed to shout in the summary,or I would have).
There was also a King Arthur series made in the UK in the 1970s to which the same thing happened. That one had also appeared on "Once Upon a Classic" on PBS; which was a show like "Masterpeice Theater," but for kids, hosted by Bill Bixby. Another show on "Once Upon a Classic" to appear on Channel 5 in the early '80s was "The Prince and the Pauper," but I don't remember that ever being on A&E. A similar miniseries that appeared on A&E in the early '80s was a live-action, taped (not filmed) version of "Ivanhoe" which I don't remember seeing before or since.