What attractions/sites do we need to book in advance for London. Too late for the keys ceremony in Tower of London. I just bought tickets for The Globe.
When?
The Churchill War Rooms often have really long lines that most tourists feel they can't afford to stand in.
Special exhibitions at museums sometimes sell out if a hot topic is involved (rock music, the royals, impressionist art, etc.)
The Sky Garden
I'm sure others can contribute more. In the meantime, this website offers a list, which I can't personally vouch for.
June of this year.
That's a busy time. If there's a specific popular play you want to see, you shouldn't wait till the day you want to see it to buy the ticket. Sometimes just a week early is fine. I get the feeling that a lot of tourists wait until they get to London to buy tickets, but that's enough for some plays to go from available to sold out for a day or two.
I haven't been to Buckingham Palace or Westminster Abbey, so I don't know about those.
The Harry Potter studio tour sells out really early.
I’d book the Houses of Parliament if that’s of interest. I doubt you’d be shut out, but you can get your choice of time.
I don’t know if Churchill War Rooms are still as popular, they definitely were after all the Churchill films a couple years ago.