British, in playing golf, say, mostly not going well (2,3,5)
I believe the answer is:
on the blink
'not going well' is the definition.
(on the blink means malfunctioning)
'british in playing golf say mostly' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'in' is an insertion indicator.
'playing golf say' becomes 'on the links' (a links is a golf course).
'mostly' means to remove the last letter.
'onthelinks' with its last letter removed is 'onthelink'.
'b' going within 'onthelink' is 'ON THE BLINK'.
(Other definitions for on the blink that I've seen before include "Not working properly" , "out of order" , "getting poor reception" .)