Servers with first-class locks (10)

I believe the answer is:

waitresses

'servers' is the definition.
(waitress is a kind of server)

'with first-class locks' is the wordplay.
'with' becomes 'w' (abbreviation).
'first class' becomes 'ai' (A1 - top quality).
'locks' becomes 'tresses' (I've seen this before).
'w'+'ai'+'tresses'='WAITRESSES'

I've seen this clue in The Telegraph.

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