Hail Newcastle as 'surprisingly spotless' (5,2,1,7)
I believe the answer is:
clean as a whistle
'spotless' is the definition.
(I've seen this in another clue)
'hail newcastle as surprisingly' is the wordplay.
'surprisingly' is an anagram indicator (a surprising ordering of the letters).
'hail'+'newcastle'+'as'='hailnewcastleas'
'hailnewcastleas' anagrammed gives 'CLEAN AS A WHISTLE'.
(Other definitions for clean as a whistle that I've seen before include "Deal with obstruction in pipe" , "Totally innocent" , "completely empty?" , "Extremely free of dirt" , "with minimal mess" .)