"OK chaps, we have enough money to run 4 Squadrons of Typhoons if you are happy to look out of the window and hope for the best or we can fit collision warners to 3 squadrons of Typhoons. What shall we do?"
Question doesn't arise. Affordability is not a legitimate consideration. And it is already known the cost is well within what MoD
is permitted to consider. DV's point, I think, is that most would like to see the ALARP (Temporal) argument tested in court. To my knowledge, it is at least 33 years since MoD started looking at a CWS for Tornado. As that was a specific technology, I'm fairly certain that requirement would have been arrived at by previous work. That's a hell of a time to carry a known risk while claiming it is ALARP because it is under consideration. Co-incidentally, I've just received a letter today saying that one cannot make a complaint about such things if (in DV's example) one doesn't live in Coldstream. Which is a lovely place by the way.