Special security teams are checking all public areas along the parade route for any explosives that might have been hidden in drains, lamp-posts, traffic lights or other hiding places.
During the wedding celebrations, police will be on the ground and also in the air.
"As we get nearer to the event itself, clearly they don't want noise of a helicopter right over the top so we'll be moving away and we'll be policing the event from a distance away," said London Police Air Support Sgt. Richard Brandon.
Security officials say the event is particularly challenging because the parade route was announced several months in advance and the guest list for the wedding itself is filled with royalty, politicians and about 50 foreign heads of state.