Former Labour leader dipping into overdraft (3)
I believe the answer is:
old
'former' is the definition.
(both can mean previous)
'labour leader dipping into overdraft' is the wordplay.
'labour leader' becomes 'l' (the leading letter of 'labour').
'dipping into' means one lot of letters goes inside another.
'overdraft' becomes 'od'.
'l' inserted into 'od' is 'OLD'.
(Other definitions for old that I've seen before include "No longer young" , "Stale" , "At an early stage - at a late stage" , "Former; aged" , "Long-established" .)