Politician about to sleep in your holiday (3,6)
I believe the answer is:
yom kippur
'holiday' is the definition.
(I have seen 'Jewish holiday' mean 'yom kippur' so perhaps 'holiday' could also mean 'yom kippur')
'politician about to sleep in your' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'about' means one lot of letters goes inside another.
'to sleep' becomes 'kip' (synonyms).
'in' means one lot of letters goes inside another.
'mp' placed around 'kip' is 'mkipp'.
'mkipp' going into 'your' is 'YOM KIPPUR'.
(Other definitions for yom kippur that I've seen before include "Jewish holiday, also called Day of Atonement" , "Holiest fast day of the Jewish calendar" , "Day of atonement, Jewish festival" , "Annual solemn Jewish Day of Atonement" , "Jewish Day of Atonement, most solemn of the year" .)