First broadcast between September 1956 and April 1957, this is another of those really early ITC swashbuckler series from the dawn of television. Amazingly, some of the episodes are in colour!
The main character, Sir Lancelot, is played by none other than Ian Chesterton himself, Sir William Russell. As a lead, Sir Lancelot is somewhat akin to Monkey (from, er, Monkey), as he is basically invincible in combat - regularly taking on up to three opponents at once in a 'fair' fight, and only ever losing if attacked from ambush or otherwise taken by surprise. As such a lot of plots involve keeping him from fighting until the very end, when he naturally wins through. Also Russell portrays Lancelot as loving to fight, swinging his two-handed sword with a big grin on his face - a very Monkeyish trait.
The second main character is Lancelot's squire, Brian. Brian is something of an audience identification character, being young and learning about the world of King Arthur, Camelot, knights, and so on, and being younger he tends to get the focus in plots and situations where, were Sir Lancelot in his place, the knight would just win straight away. This is done well for the most part, but a few of the earlier episodes give too much attention to Brian - it's Sir Lancelot we want to watch, dammit, the clue's in the name!
The third main regular character (there are other regulars, including King Arthur, Queen Guinevere and Sir Kay, but they are seldom the protagonists of episodes, instead serving more like plot devices for the most part - sending Sir Lancelot on his quest of the week, that kind of thing) is Merlin the Magician. Once of my favourite things about the series is that there is almost no magic - a far cry from most versions of the King Arthur legend I am familiar with. Merlin is more like a scientist, his magic comes from his knowledge of things like invisible ink, carrier pigeons, and other advances. (The only real 'magic' in the series is a form of mind-control hypnosis employed by Morgana and countered by Merlin - a single instance from 30 stories, and even that is a sort of TV hypnosis that you might see in something like The Avengers.)
Sir Lancelot is an intelligent character, capable of seeing Merlin's tricks for what they are, and from their first meeting they become friends and treat each other as equals. Their relationship is not a million miles from that between the Doctor and Ian after it settles down in Doctor Who's second season - the more experienced scientist and his pupil. It sets this series up on another level and it may be my the reason this has become my favourite of the four ITC swashbuckling series I have watched so far.
Being a very old series from the 1950s, there are only a few guest stars I recognise. The main one has to be Patrick McGoohan, playing the villain-of-the-week in episode 4. Sadly, while he is fine (and is instantly recognisable), it is one of the weakest stories of the whole run, and not an episode I would recommend if you want to get a taste of the series.
At the other end of the run we see Jerome "Stevens" Willis doing an Irish accent as the Prince of Limerick.
There's something of a repertory feel to the early episodes, with the same actors cropping up again and again in different roles from week to week. As such Derren Nesbitt and Nigel Green show up repeatedly, often playing villains-of-the-week, their henchmen, or just some random knight, blacksmith or villager that Sir Lancelot encounters.
With 30 self-contained episodes of only 25 minutes' duration, the writers do well to vary the plots and, for the most part, avoid cliches. There are perhaps a few too many princesses who want to marry against their father's will, but otherwise it's fine - better than contemporary series The Count of Monte Cristo at any rate.
I can't end without mentioning the theme music. While the opening titles are an average, unmemorable example of exactly the sort of thing you'd expect for this type of series, the end music is something else entirely... the word "twee" doesn't begin to describe it. Most of the series seems to be available on YouTube if you want to experience it for yourself, though the full song seems to only be on the early, black and white ones - a mercifully abbreviated version of one verse and the chorus is all you get to close the colour eps.