Well, after last time, they are now off planet... but it's not getting better. This is A Much Needed Holiday.
The TPs are sent on holiday to another planet (which is a clear studio set) to examine archaeology ruins, but as it happens an alien race is on this planet making the local young boys into a slave force. (A lot has been said about Roger's proclivities towards having young boys in rather skimpy outfits, but I'll leave that to the commentaries.) Of course, the TPs have to get involved, and it's only through them that the small team of aliens are overthrown.
Another planet, another rebelling. According to the commentary, this was in a novel, then a Look In strip, and now an episode. And yet... it feels like a low cut rate knock off Doctor Who episode. Complete with rather rubbish looking aliens (in that the aliens look like they are wearing rubbish bags, with silver foil heads and hands).
This just feels so generic, it a) could be in any series, and b) wouldn't be a good episode in any series.