Beg Irish somehow to accept British nonsense (9)
I believe the answer is:
gibberish
'nonsense' is the definition.
(gibberish is a kind of nonsense)
'beg irish somehow to accept british' is the wordplay.
'somehow' indicates an anagram.
'to accept' is an insertion indicator.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'beg'+'irish'='begirish'
'begirish' with letters rearranged gives 'giberish'.
'giberish' enclosing 'b' is 'GIBBERISH'.
(Other definitions for gibberish that I've seen before include "moonshine" , "Gobbledygook" , "Nonsensical talk" , "Rubbish" , "Tosh" .)