Repeating it, English traitor in Gateshead (9)
I believe the answer is:
iterating
'repeating' is the definition.
('iterate' can be a synonym of 'repeat')
'it english traitor in gateshead' is the wordplay.
'english' becomes 'E' (abbreviation).
'traitor' becomes 'rat' (rat can mean a treacherous person).
'gateshead' becomes 'g' (head letter of 'gates').
'it'+'e'+'rat'+'in'+'g'='ITERATING'
(Other definitions for iterating that I've seen before include "Repeating" , "Repetition" .)