Dandy left inside joint (6)
I believe the answer is:
spliff
'joint' is the definition.
(both can mean a cannabis cigarette)
'dandy left' is the wordplay.
I cannot really understand how this works, but
'left' could be 'l' (common abbreviation) and 'l' is found within the answer.
The remaining letters 'spiff' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'inside' acts as a link.
Can you help me to learn more?
(Other definitions for spliff that I've seen before include "Cannabis joint" , "Joint (for smoking)" , "Marijuana fag" , "Dodgy smoke" , "Blow in this tube" .)