Flag is pentagon, surprisingly divided by five (6,5)

I believe the answer is:

paving stone

'flag' is the definition.
(flagstone)

'is pentagon surprisingly divided by five' is the wordplay.
'surprisingly' indicates anagramming the letters (a surprising ordering of the letters).
'divided by' is an insertion indicator.
'five' becomes 'V' (Roman numeral).
'is'+'pentagon'='ispentagon'
'ispentagon' anagrammed gives 'paingstone'.
'paingstone' placed around 'v' is 'PAVING-STONE'.

(Another definition for paving stone that I've seen is " Slab".)

I've seen this clue in The Telegraph.

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