Severe, man. Severe.

Following (several years after) the lead of the US (as they do too often), the UK today introduced one of these thoroughly useless Terror Threat Level Indicators:

Today, the level is SEVERE, meaning: "an attack is highly likely." Or, possibly meaning: "we don't know shit; please don't yell at us if bad things happen."

Should it ever be moved up one, to the top level of CRITICAL, what should I do? If "an attack is expected imminently" I feel as tho there is something I should be doing, something other than peeing my pants.

This is what they say in their "How the Public should respond" section:

Public vigilance is always important regardless of the current national threat level, but it is especially important given the current national threat. Sharing national threat levels with the general public keeps everyone informed and explains the context for the various security measures (for example airport security or bag searches) we may encounter as we go about our daily lives.

Wait, so this is just an excuse to search my bag? Shit. Better come out from under the bed, then.