London area to surrender and break away (6)
I believe the answer is:
secede
'break away' is the definition.
(I know that break away can be written as secede)
'london area to surrender' is the wordplay.
'london area' becomes 'SE' (abbreviation for South East).
'to surrender' becomes 'cede' (synonyms).
'se'+'cede'='SECEDE'
'and' is the link.
(Other definitions for secede that I've seen before include "Formally withdraw (from federal union)" , "Withdraw from political union" , "Withdraw from, say organisation" , "'Withdraw formally, from a political body perhaps (6)'" , "Disaffiliate" .)