"Lobster" wrote in message
...

I suppose one issue to consider is what happens if someone wants to
install cavity wall insulation at a later date... if the cable is
unprotected within the cavity, it will likely come into contact with
polystyrene insulation, causing instant disintegration(?) of the outer
sheath...

No.
The plasticizer causes the polystyrene to shrink away from the cable so it
breaks contact.
Assuming your polystyrene is bonded together like it should be.

Mines been OK for the last 25 years, I'll let you know if anything happens.