Ill-gotten gains of a swollen headed humorist (4)

I believe the answer is:

swag

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'ill-gotten gains' is the definition.
(swag can mean items stolen in a robbery)

'swollen headed humorist' is the wordplay.
'swollen' becomes 'sw' (I can't explain this - if you can you should give a lot more credence to this answer).
'headed' means to remove the first letter (head can mean to remove the top from something).
'humorist' becomes 'wag' (wag is a kind of humorist).
'wag' with its first letter taken off is 'ag'.
'sw'+'ag'='SWAG'

'of a' acts as a link.

Can you help me to learn more?

(Other definitions for swag that I've seen before include "Burglar's loot" , "Thief's bundle" , "pack of Aussie travellers" , "goods from burglary" , "Burglar's haul" .)

I've seen this clue in the Evening Standard.

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