Long flag extracted from both ends of blue post (9)

I believe the answer is:

banderole

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

'long flag' is the definition.
'banderole' can be an answer for 'flag' (I've seen this before). I am unsure of the 'long' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for banderole that I've seen before include "Flag" , "Renaissance feature" .)

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app