London area sadly often heaving, overcrowded, first of all (4)
I believe the answer is:
soho
'london area' is the definition.
(I've seen this before)
'sadly often heaving overcrowded first of all' is the wordplay.
'first of all' suggests taking the first letters.
The first letters of 'sadly often heaving overcrowded' is 'SOHO'.
(Other definitions for soho that I've seen before include "Entertainment district in London's West End" , "Colourful show-biz area of West End London" , "Colourful district in central London" , "London's former Bohemia" , "fashionable neighbourhood (or neighborhood)" .)