Alarming changes ready to overwhelm a nervous MP here? (8,4)

I believe the answer is:

marginal seat

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'nervous mp here?' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'alarming changes ready to overwhelm a' is the wordplay.
'changes' is an anagram indicator.
'ready' becomes 'set' (set can mean ready or prepared).
'to overwhelm' is an insertion indicator.
'alarming' with letters rearranged gives 'marginal'.
'marginal'+'set'='marginalset'
'marginalset' enclosing 'a' is 'MARGINAL SEAT'.

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(Other definitions for marginal seat that I've seen before include "Scene of electoral uncertainty" , "Constituency liable to change hands" .)

I've seen this clue in The Telegraph.

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