Going up to play organ inside for a sovereign (5)
I believe the answer is:
royal
'for a sovereign' is the definition.
(I've seen this in another clue)
'going up to play organ inside' is the wordplay.
'going up' says the letters should be written backwards (in a down clue, the letters are written upwards).
'inside' indicates the answer is hidden within the clue.
'layor' is hidden within 'to play organ'.
'layor' reversed gives 'ROYAL'.
(Other definitions for royal that I've seen before include "Sort of jelly, flush or blue" , "Befitting a monarch" , "Regal, majestic," , "Referring to the sovereign" , "Shade of blue" .)