Sanctimonious inspectors going into a Vauxhall plant (10)
I believe the answer is:
aspidistra
'plant' is the definition.
(aspidistra is a kind of plant)
'sanctimonious inspectors going into a vauxhall' is the wordplay.
'sanctimonious' becomes 'pi' (old-fashioned term for pious).
'inspectors' becomes 'dis' (DIs, detective inspectors).
'going into' means one lot of letters goes inside another.
'a vauxhall' becomes 'astra' (I am not sure about this - if you are sure you should believe this answer much more).
'pi'+'dis'='pidis'
'pidis' placed inside 'astra' is 'ASPIDISTRA'.
Can you help me to learn more?
(Other definitions for aspidistra that I've seen before include "Household growth" , "something normally developed in-house?" , "Huge house plant" , "Iris adapts (anag) - indoor plant" , "Large houseplant" .)