It's NOT the most successful British movie ever.
The use of the word 'ever' is completely misplaced - simply because at some point it will be overtaken by the next British blockbuster.
And please remember - if you are going to base box office performance on money rather than actual number of tickets sold, then OF COURSE the latest big movie will outperform the previous ones...simply because ticket prices go up every year.
So it's obvious the latest blockbuster will always out-perform the previous one in terms of money earned. But that has nothing whatsoever to do with the quality of the movie, merely that the marketing department have done their job and convinced people that they HAVE to go and see THAT movie.
Box office performance should always be based on admissions, not money.