It might not be something you don't want to go back to, but it was developed out of necessity, and if things ever got heavy again then Napalm and Landmine stocks would be topped up.
We have all experienced how peacetime brings out the worst in military and particularly government doctrine and procurement.
Edit: Didn't read the IS connection. The Question to that is: 'Is what we currently stock capable?' I would say yes.
Though, The cheapest way for the British government to do 'Terror' is to grow some balls.