This one is SF at its best. You take a concept, and idea, and then work it into a tale, or a yarn as they used to say in Ancient Times.
The Doctor was hardly in this episode proving that it is still possible to have the star invisible for a whole story and yet still be the star. Catherine Tate was excellent and some very heavy concepts got worked into the story, such as the "England for the English" scene. Very poignant and worthy of discussion with the kids.
Billie Piper was there as well, and very nice too. Should they have brought her back? Well why not, who could resist...
