Groups of people, some of them grannies? (5)

I believe the answer is:

knots

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'grannies?' is the definition.
(granny is a kind of knot)

I can't explain the rest of the clue.

(Other definitions for knots that I've seen before include "Nautical mph" , "Tangles" , "Looped fastenings" , "the going rate, in the main" , "They secure" .)

I've seen this clue in the Evening Standard.

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