Urgent message about British politician, a tale of woe (3,5)
I believe the answer is:
sob story
'a tale of woe' is the definition.
(I've seen this before)
'urgent message about british politician' is the wordplay.
'urgent message' becomes 'sos'.
'about' means one lot of letters goes inside another.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'politician' becomes 'tory' (I've seen this before).
'sos' placed around 'b' is 'sobs'.
'sobs'+'tory'='SOB-STORY'
(Other definitions for sob story that I've seen before include "attempt to gain sympathy" , "Tale of misfortune" , "unhappy tale" , "Tale to gain sympathy" , "Affecting tale (colloq.)" .)