Swelling finished, become unrestrained (4,4)

I believe the answer is:

boil over

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'become unrestrained' is the definition.
I can't tell whether this defines the answer.

'swelling finished' is the wordplay.
'swelling' becomes 'boil' (I can't explain this - if you can you should believe this answer much more).
'finished' becomes 'over' (similar in meaning).
'boil'+'over'='BOIL OVER'

Can you help me to learn more?

(Other definitions for boil over that I've seen before include "Become so excited as to lose control" , "Seethe uncontrollably" , "Evil boor (anag.)" , "Hit the roof" , "maybe get too passionate" .)

I've seen this clue in The Daily Express.

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