Like many similar government programs, it was thoughtfully designed.

The biggest risk in any national emergency is panic. As seen recently with Covid and earlier, when a rumour toilet roll supplies running out. Mass panic trigger irrational behaviour en masse which is bad news all round.

Second thing, and related I suppose, is the fear level of the populace. If the message is That “things will be difficult but good old British common sense will prevail, while the government sorts things out for you”. The government keeps people, voters, on side . Alternatively, the government come under a lot more scrutiny if it’s widely understood to be ‘game over’ if war in not averted.

So while you cannot rely on these to be truthful or factually accurate, or even designed to keep you alive , you can be reasonably be sure it’s part of a plan.

In 196 Raymond Briggs wrote a graphic novel , which became a movie - called “when the wind blows” that pretty much nailed this.

There are clips on YouTube but nothing substantial. If you get chance to see it - do so.