Call for help interrupted by British politician's tale of woe (3,5)
I believe the answer is:
sob story
'tale of woe' is the definition.
(I've seen this before)
'call for help interrupted by british politician's' is the wordplay.
'call for help' becomes 'sos' (I've seen this before).
'interrupted by' indicates putting letters inside.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'politician' becomes 'tory' (I've seen this before).
'sos' enclosing 'b' is 'sobs'.
'sobs'+'tory'='SOB-STORY'
(Other definitions for sob story that I've seen before include "A tale of woes" , "Tear-jerking account" , "Pitiful tale told to arouse sympathy" , "Tale of misfortune" , "appeal to emotions" .)