Whilst making the current Doctor Who episode, Master of Dimensions, I had a scout around After Effects tutorial videos for special effects used in the film. One tutorial showed how to make used of a chromakey effect in After Effects called Keylight. This is a chromakey effect that compared to Premiere Pro is more advanced, efficient and easier to apply.
Keylight resulted in episode Doctor Who episodes to be re-edited so the quality of effects remain consistent throughout as shown in the following comparison frames. This also opened opportunities to correct other effects and background.
The new versions of the episodes 2 to 4 can be watched below.