Furthest route changed on flash street (9)

I believe the answer is:

outermost

'furthest' is the definition.
(thesaurus)

'route changed on flash street' is the wordplay.
'changed' is an anagram indicator.
'on' is a charade indicator (letters next to each other).
'flash' becomes 'mo' (I've seen this in other clues**).
'street' becomes 'st'.
'route' with letters rearranged gives 'outer'.
'outer'+'mo'+'st'='OUTERMOST'

(Another definition for outermost that I've seen is " farthest from centre".)

I've seen this clue in The Telegraph.

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