I wish the UK good luck with their alert tests. But do the people really, truly understand the difference between an "Extreme" alert and a "Severe" alert? I bet the average person doesn't. We have the same issue here in this country, and likely most countries do as well. They wind up creating several different levels of alerts, giving those alert types ambiguous names, never really fully explaining them, then wondering why we simply ignore them. It would be better to use easy to understand alerts like "there is a slight chance you might get struck by small hail stones today" or "get in the basement now or kiss your backside goodbye!" Instead they tend to say a "severe alert" or something equally ambiguous. Then we talk among ourselves and try to remember what a "severe" alert actually means trying to remember just how alert we should now be. In the US after the 9/11 attacks, the idiots in Washington decided to use colors to differentiate the levels of alertness, but few people ever really understood just what a orange or purple alert was in relation to a yellow or red alert. The result was predictable, we ignored the alerts because they were confusing.
In the US they issue weather alerts, which is a very good idea if done sensibly. But expecting a large, government bureaucracy to be sensible is a lessen in futility. We get alerts for our local area, but unfortunately we also tend to get alerts for areas that or up to 50 or more miles away. During spring we constantly get alerts, and there is nothing but sunshine outside. The alerts were from two counties over and of no concern. Again the result is the same, we begin to ignore the alerts.
If a child is abducted in you area, by all means get an alert and be on the lookout. If the child was abducted 1000 miles away, well do we really need that ear piercing alert over our phone? Probably not. The result is we get way too many unrelated alerts and thus start ignoring them, even if we shouldn't.