Published British newspaper best when boasting (7)
I believe the answer is:
outbrag
'best when boasting' is the definition.
I can't tell whether this definition defines the answer.
'published british newspaper' is the wordplay.
'published' becomes 'out' (a published book is 'out').
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'newspaper' becomes 'rag' (informal term for a newspaper).
'out'+'b'+'rag'='OUTBRAG'
Can you help me to learn more?
(Another definition for outbrag that I've seen is " Make yourself seem better".)