Men, in principle, responsible for a block of flats (8)
I believe the answer is:
tenement
'a block of flats' is the definition.
(I've seen this before)
'men in principle' is the wordplay.
'in' indicates putting letters inside.
'principle' becomes 'tenet' (I've seen this before).
'men' inserted into 'tenet' is 'TENEMENT'.
'responsible for' acts as a link.
(Other definitions for tenement that I've seen before include "Building containing several dwellings" , "Rented accommodation" , "Dwelling-place" , "Building divided into several residences" , "Run-down dwelling housing many people" .)