Process by which to stop one going round the welfare centre (8)

I believe the answer is:

halftone

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'process by which' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'stop one going round the welfare centre' is the wordplay.
'stop' becomes 'halt' (halt can mean to stop).
'going round' is an insertion indicator (some letters go around others).
'centre' indicates the central letters.
The centre of 'welfare' is 'f'.
'halt'+'one'='haltone'
'haltone' placed around 'f' is 'HALFTONE'.

'to' acts as a link.

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I've seen this clue in the Evening Standard.

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