Ask me what the biggest premiere London has ever had, and it's not even close. It was the premiere for Harry Potter and the Deathly Hallows Part 2 back in 2011. I've been to premieres where Leicester Square was full. I've been to premieres where Leicester Square was full and and a whole side of the square was also full.... and I was even at one where the premiere took up all of the middle of the square AND then fed two separate cinemas.
But imagine the last one of those and then add ALL of Trafalgar Square to it. And then run a carpet to connect the two, and close down the road next to Trafalgar Square and let it be filled with people on top of the ones in Trafalgar Square (some of whom had camped since MONDAY for a Thursday evening premiere), and the ones in Leicester Square.
And then imagine you worked a regular job and wanted to take photos at that event and couldn't merely not camp out... but had to go to work THAT DAY.
Well... I did. Only because my boss let me out early, and due to the aforementioned last-minute road closure, and the fact that the step-stool I had plus a long zoom on the Pentax gave me an almost unobstructed view of the main stage (because you need to plan for the worst while hoping for the best).
And it was big. And I was there. And I was... kind of glad, actually. And going back and recreating the journal took about 3 times longer than any other journal I've done for this site...
Also added : Kung Fu Panda 2 (featuring Jack Black!), Larry Crowne (featuring not just Tom Hanks, but The Hoff and A Rolling Stone!), Shrek The Musical (featuring nobody from the movie nor the animated series it was based on), Cars2 (Michael Caine at least showed up), Horrible Bosses (featuring Jennifer Aniston and Jason Bateman), Horrid Henry (featuring who?), and The Devils Double (featuring Iron Man's Dad)
But honestly? Harry Potter and The Deathly Hallows Part 2 redefined "Big" in a way that I'd have difficulty imagine you could duplicate.