Labour's got a new catchphrase (6)
I believe the answer is:
slogan
'catchphrase' is the definition.
(eg a political catchphrase)
'labour's got a new' is the wordplay.
'labour's got' becomes 'slog' (I can't justify this - if you can you should believe this answer much more).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'slog'+'a'+'n'='SLOGAN'
Can you help me to learn more?
(Other definitions for slogan that I've seen before include "advertising catch phrase" , "Rallying cry" , "Memorable advertising phrase" , "Short catchy phrase used in advertising" , "Logo" .)