I grew up in the 70's in a Greater London suburb, at the height of IRA activities, then working in a supermarket we regularly received bomb threats, we had to take each threat seriously even though we knew that is was a shoplifting scam, that in the mass exodus through the doors shoplifters were exiting with goods unpaid for.
Several years later my then airline employer went thru a spate of bomb threats, somebody who had a grudge against the airline or our MD in particular, each threat was left to the decision of the commander and eventually the commanders ignored the threats not just receiving the praise and gratitude of our MD but the threats ultimately stopped once they realised they were no longer being taken seriously.