Excerpt from the Chaos Pool:
The White Guardian summons Astra and orders her to bring him the Key, but she refuses. The Black Guardian orders the unnamed woman to do the same, but she announces that her name is Freedom and she is free of his control at last. The Doctor realises that because the two Guardians are evenly matched, they both need the help of someone else in order to give them the edge.
I’m not saying that everything matches 100 percent but you don’t have to be a genius to see that these events are similar and when put together with the mounting stack of other similarities that I have found you would have to be pretty gullible to believe that this is still a coincidence.
If you want to read the stories for yourself they can be found at the following locations:
The Judgement of Isskar:
The Destroyer of Delights:
The Chaos Pool: