Having long standing supporters (5)

I believe the answer is:

leggy

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'long standing supporters' is the definition.
'leggy' can be an answer for 'long' (thesaurus). I am unsure of the 'standing supporters' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for leggy that I've seen before include "(Of a plant) tall and straggly" , "Attractively tall?" , "(Of plant) having a long stem" , "Long, slender" , "with long pins" .)

I've seen this clue in the Evening Standard.

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