For this somewhat amazing finale (well, at least in comparison to the whole Journey's End and Last of the Timelord crappiness...), the last episode got 5.1m views (31% of the overall audience which I personally think was too little - it really was a good episode!)
and the penultimate one got 5.9m, which I don't really understand because apart from the fact that many people were probably at the beach this weekend, it still doesn't explain why so little people watched such a brilliant episode!!
