Factual error: Apparently, Ratigan had to cross the River Thames to reach Big Ben from Buckingham Palace as evidenced by him tossing Fidget into the river before taking reign of the blimp. However, the two landmarks are on the same side of the river.
Suggested correction: Ratigan changed direction multiple times during the chase because he was trying to get away from Basil. He may have flown away from that side of the river, but then after changing direction he flew across to the side he came from again.