Welsh papers stop including English spread (7)
I believe the answer is:
widened
'spread' is the definition.
(thesaurus)
'welsh papers stop including english' is the wordplay.
'welsh' becomes 'W' (abbreviation).
'papers' becomes 'ID' (identifying documents are one's 'papers').
'stop' becomes 'end' (synonyms).
'including' is an insertion indicator.
'english' becomes 'E' (abbreviation).
'end' placed around 'e' is 'ened'.
'w'+'id'+'ened'='WIDENED'
(Other definitions for widened that I've seen before include "Expanded" , "Given more breadth" , "Made broader" .)