Boring type of car - those who have one are certain to stay in the house (4,4)
I believe the answer is:
safe seat
'those who have one are certain to stay in the house' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'boring type of car' is the wordplay.
'boring type of' becomes 'safe' (I can't justify this - if you can you should give a lot more credence to this answer).
'car' becomes 'SEAT' (make of car).
'safe'+'seat'='SAFE SEAT'
Can you help me to learn more?
(Other definitions for safe seat that I've seen before include "Constituency MP prefers" , "What the Uxbridge and South Ruislip constituency is for Boris" , "MP's desire" , "What politician would like" , "Constituency odds-on to be retained at an election" .)