Hair gel a cop recovered in islands (11)

I believe the answer is:

archipelago

I'm a little stuck... Click here to teach me more about this clue!

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

'hair gel a cop recovered' is the wordplay.
'hair gel a cop' anagrams to 'ARCHIPELAGO'.
But, I am not sure how the anagram is indicated.

'in' is the link.

Can you help me to learn more?

(Other definitions for archipelago that I've seen before include "Bahrain, for one" , "the Philippines maybe" , "Cluster of islands" , "Extensive group of islands" , "Philippines, say" .)

I've seen this clue in The Everyman puzzle in The Observer.

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