Why were three episodes missing on the UK Video releases?

So the UK release of videos had six volumes. Which presumably held all episodes of Season One and Two. However the first three volumes representing Season One had the episode "Three Lessons" missing from it. The last three volumes representing Season Two had episodes "Prow Beaten" and "Barga's Rival" missing from it.

Any idea why they did this? I remember being so disappointed when I first watched the videos. Barga's Rival was one of my favourite episodes as a child. The other two episodes I had never seen before.

Of course, every episode is on YouTube now and I have watched and rewatched them a few times. But still I'm curious to know if there's a specific reason why those three episodes were cut?