Parliamentary celebrations at the start of 14 across for Sinn F?in and The Greens (5,7)

I believe the answer is:

house-parties

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'the start of 14 across for sinn f?in and the greens' is the definition.
I know nothing about this answer so I can't judge whether this works.

'parliamentary celebrations' is the wordplay.
'parliamentary' becomes 'house' (I can't justify this - if you can you should give a lot more credence to this answer).
'celebrations' becomes 'parties' (I've seen this before).
'house'+'parties'='HOUSE-PARTIES'

'at' acts as a link.

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I've seen this clue in the Irish Times.

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