You don’t need to know this
The security threat level against this country has been downgraded from severe to substantial.
I’m not sure what you can do with that information: stop wearing your flak jacket, start travelling on the Underground, smile at people you may have previously thought were terrorists?
If the threat is “Substantial” it means that an attack on British soil is a “strong possibility”. That will not make me sleep any easier so I don’t want anyone telling me the threat is downgraded.
It just doesn’t make sense to me to inform the country that the threat is reduced when we are fighting a war to prevent the spread of terror. As for the useful advice of to “Remain Vigilant” – what on earth does that mean?
But of course if I was a terrorist I might feel different. Certainly the IRA did as most of their outrageous attacks occured when the threat level had been reduced. Don’t we learn anything from history?