Heads for Tower Hamlets: spots a party (6)
I believe the answer is:
thrash
'a party' is the definition.
(informal term for a party)
'heads for tower hamlets spots' is the wordplay.
'heads for' suggests taking the first letters (I've seen 'head for' mean this).
'spots' becomes 'rash' (I've seen this before).
The initial letters of 'tower hamlets' is 'th'.
'th'+'rash'='THRASH'
(Other definitions for thrash that I've seen before include "Beat violently" , "Decisively beat" , "Flog; party" , "Lay on - party" , "Hit hard" .)