So hard to get round part of London (4)
I believe the answer is:
soho
'part of london' is the definition.
(district of Westminster)
'so hard to get round' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to get round' becomes 'o' (I've seen this in other clues).
'so'+'h'+'o'='SOHO'
(Other definitions for soho that I've seen before include "London's nightlife centre" , "London square" , "Colourful neighbourhood in London's West End" , "W London area" , "fashionable neighbourhood (or neighborhood)" .)