It is demonstrably non-contributory because if you opt out of it (I have no idea why you would) then you still get paid the same. It also does not squirrel away a pension pot for you. It is in effect an IOU note from the Government, written into UK Law, to keep paying you in retirement. It is paid for out of separate fund propped up by the Defence Budget. The country would need to descend into total Anarchy or go totally bankrupt (after all of its assets had been sold off) to not pay out.
Of course there will be those that say this could be possible - of course it could, but how likely is that compared to your pension fund company going belly up, your stocks and shares taking a dive, or your property portfolio spoofing in? I’d suggest that all of the latter are very much more likely!