To be completely fair, you cannot attribute ALL of those to Gaga & Tony. Strictly v X Factor is a common thing in the UK and the reason X Factor had better ratings last week (besides being the superior show obviously

) is because it was the FIRST live results show. Since X Factor went down by 500k? and Strictly up by 620k, we can estimate that 500k was because it's no longer the first live results, and the remainder (120k) from Tony and Gaga.
Nevertheless good for them
