Constituency must keep network impenetrable with this preparation (7)
I believe the answer is:
sealant
'impenetrable with this preparation' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'constituency must keep network' is the wordplay.
'constituency' becomes 'seat' (House of Commons seats represent constituencies).
'must keep' indicates putting letters inside.
'network' becomes 'LAN' (Local Area Network).
'seat' going around 'lan' is 'SEALANT'.
Can you help me to learn more?
(Other definitions for sealant that I've seen before include "closer?" , "Material for making airtight or watertight" , "Material blocking leaks" , "Material used for an airtight or watertight join" , "Mastic maybe" .)