Disposed off major reference work about political party (5)

I believe the answer is:

offed

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'disposed off major' is the definition.
The definition suggests a past participle verb which matches the answer.

'reference work about political party' is the wordplay.
'reference work' becomes 'OED'.
'about' indicates putting letters inside.
'political party' becomes 'ff' (Fianna Fail).
'oed' placed around 'ff' is 'OFFED'.

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I've seen this clue in The Irish Times.

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