Top Union appointment protects millions (6)

I believe the answer is:

upmost

'top' is the definition.
(similar in meaning)

'union appointment protects millions' is the wordplay.
'union' becomes 'U' (common abbreviation as in 'Trades Union Congress').
'appointment' becomes 'post' (appointment to a job).
'protects' means one lot of letters goes inside another (outer letters protect inside letters).
'millions' becomes 'm' (abbreviation).
'post' placed around 'm' is 'pmost'.
'u'+'pmost'='UPMOST'

I've seen this clue in The Independent.

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