In this context the Doctor and Companions find themselves in a Saxon village on the coast. But all is abnormal because there is a Monk nearby who'd taken residence in an abandoned Monastery, and this Monk had strange artifacts in his possession. Such as a wristwatch, a Victrola with which to play monks chants, an electric hotplate and electric toaster, a pair of binoculars, a ballpoint pen, and a bazooka. This was no normal Monk, and perhaps not a Monk at all.
Turns out the Question in this story is in the title. Can one or should one meddle in time? So far the Doctor has claimed the moral high ground of not meddling in the events he goes to witness. For example this was clearest in The Aztecs where Barbara clearly wanted to meddle with the outcome of that civilization. The Monk is also a fellow time traveler, he has his own TARDIS, a newer model than the Doctors, but he has a totally different attitude. To have great fun changing the events of history.
In this case he thinks King Harold Godwinson is a good man, would make a great leader, and he thinks with a little bit of nudging the development of society could be speeded up. Such that, for instance, Shakespeare's plays could be delivered first on Television. Eep!
Again the Doctor is able to take the moral high ground, and takes it as the utmost importance to stop the Meddler.
Hmm, the Question then seems to be does bringing in any outside influence modify events in any way? In this case the presence of the Doctor and Companions would have had little effect on history. But in other series there's a big effect. Such as their presence at the Space Museum which enabled the indigenous inhabitants of that planet successfully revolt against the invaders. Within the context of Doctor Who the makers of the show are presenting inconsistency, in some cases the Doctor is able to say "no meddling" but in other cases the Doctor is meddling big time.
Well, okay, so how often did the crew of the Enterprise violate the Prime Directive?
And really it's just a TV show. Honest.