Upset around Gunners increased (9)

I believe the answer is:

spiralled

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'increased' is the definition.
Although both the answer and definition are past participle verbs, I don't see how one could define the other.

'upset around gunners' is the wordplay.
'upset' becomes 'spilled' (I've seen this in another clue).
'around' indicates putting letters inside.
'gunners' becomes 'RA' (Royal Artillery).
'spilled' going around 'ra' is 'SPIRALLED'.

Can you help me to learn more?

I've seen this clue in The Independent.

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