March for breakaway? Not Home Counties (10)
I believe the answer is:
procession
'march' is the definition.
(thesaurus)
'for breakaway? not home counties' is the wordplay.
'for' becomes 'pro' (I've seen this before).
'breakaway?' becomes 'secession' (breakaway is a kind of secession).
'not' suggests deleting specific letters.
'home counties' becomes 'se'.
'secession' with 'se' taken out is 'cession'.
'pro'+'cession'='PROCESSION'
(Other definitions for procession that I've seen before include "Parade, cavalcade" , "Motorcade" .)