This afternoon, standing outside New Scotland Yard, Metropolitan Police Assistant Commissioner John Yates said it was "absolutely vital" that the public remained vigilant.
"...what I would say is that with the current threat level in the UK at severe and with the information we have, I believe today's arrests were absolutely necessary in order to keep the public safe."
So the threat level is severe is it? Let's take that at face value. Either the threat level is (1) related to the information and allegations involved in these arrests, or (2) unrelated to them.
If it's (1), then citing the threat level is blatant double-counting - you have the information, and the fact that as a result the 'threat level' has been increased is a side-effect, not an additional cause for concern.
If it's (2), then the threat level is irrelevant.
In either case, there's an odd kind of fetishisation of this Threat Level. It's treated as if it were some kind of terror-barometer, a source rather than a summary of information. It's also treated as if it measured some free-floating ambient substance, 'terror-risk', which somehow ebbs and flows, casting its baleful influence quite independently of particular facts about suspects or bombs or suspicious behaviour.