Mad at flat décor ultimately concealed by Prime Minister: reason close allies lost respect? (11,6,8)

I believe the answer is:

familiarity breeds contempt

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'allies lost respect?' is the definition.
I know nothing about this answer so I can't judge whether this works.

'mad at flat decor ultimately concealed by prime minister reason close' is the wordplay.
I cannot really see how this works, but
'at' could be 'on' (location) and 'on' is found in the answer.
'close' could be 'familiar' (similar in meaning) and 'familiar' is found in the answer.
This explanation may well be incorrect...

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I've seen this clue in The Guardian.

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