Recalling a number one island (4)
I believe the answer is:
iona
'island' is the definition.
(I've seen this before)
'recalling a number one' is the wordplay.
'recalling' says the letters should be written backwards.
'number' becomes 'no' (abbreviation for 'number'**).
'one' becomes 'i' (Roman numeral).
'a'+'no'+'i'='anoi'
'anoi' reversed gives 'IONA'.
(Other definitions for iona that I've seen before include "holy site" , "Hebridean location" , "Macbeth's resting" , "Inner Hebridean island" , "one in Inner Hebrides" .)