Islanders: unknown number in bistro, drunk (7)

I believe the answer is:

britons

'islanders' is the definition.
(I've seen this before)

'unknown number in bistro drunk' is the wordplay.
'unknown number' becomes 'n'.
'in' is an insertion indicator.
'drunk' is an anagram indicator.
'bistro' is an anagram of 'britos'.
'n' placed within 'britos' is 'BRITONS'.

(Another definition for britons that I've seen is " Islanders".)

I've seen this clue in The Telegraph.

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