the mayor isn't Jewish or Hindu so it would be inappropriate for him to light the menorah or Diwali lights.  Also Ramadan and Eid is about 30 days, Hannukah is 8 nights--what's your point?  As I recall Christmas decorations are up for about 40 days all over central London.  The Ramadan lights are up from Piccadilly Circus to Leicester Square. basically one road.  Not sure what your outrage is but if you have such an issue with people who are different from you maybe London is not the city for you.