McKellen's magic role also in Blue Peter coming up? (7)
I believe the answer is:
gandalf
'mckellen's magic role' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'also in blue peter coming up?' is the wordplay.
'also' becomes 'and' (both can mean in addition).
'in' means one lot of letters goes inside another.
'blue peter coming' becomes 'flag' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'up?' says the letters should be written backwards (in down clue: letters go upwards).
'flag' backwards is 'galf'.
'and' inserted into 'galf' is 'GANDALF'.
Can you help me to learn more?
(Other definitions for gandalf that I've seen before include "Tolkien's wizard" , "Tolkien character" .)