Of London or Manchester, the bigger (7)
I believe the answer is:
greater
'the bigger' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for greater that I've seen before include "Less small" , "of more importance" , "More grand" , "Larger or more outstanding" , "More renowned" .)