London perhaps profits from a cause of taxation (7,5)
I believe the answer is:
capital gains
'a cause of taxation' is the definition.
I can't judge whether this defines the answer.
'london perhaps profits' is the wordplay.
'london perhaps' becomes 'capital' (London is an example).
'profits' becomes 'gains' ('gain' can be a synonym of 'profit').
'capital'+'gains'='CAPITAL GAINS'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for capital gains that I've seen before include "Profits from investment sales" , "Profits from the sale of assets" , "One pays tax on these" , "post-war Honolulu and Juneau for US?" , "target of 17, 8 [CHANCELLORS STATEMENT] - with 6a" .)