(catholic) Ireland Independecy war?
nobody try to conquer the Channel Isles?
Gibraltad?
the british empire go on intact?
Germany and Britain are in a tecnology war race in the 1900 and when one of them magicly fall
pass and future british nobel winners die, but german Eistein is intact
Why do you think other nations would automatically declare war on Britain? Far more likely that they send aid. It makes everyone look good. Might even butterfly away a 1914 Great War, or move it a decade or more into the future.
Ireland: Again, there needs to be some groundwork and preparations for a war of independence. A sudden catastrophe like a meteor impact doesn't give any prep time. Perhaps it could be used as an opportunity for more local governance until central government in England is restored.
Were most or any future British Nobel winners in London on that day, rather than Cambridge or elsewhere?