The more that details have emerged about Wednesday’s attack on Westminster, the more they point to the wisdom of routinely arming the police.
It is now clearer that had the officers in the vicinity of Khalid Masood during his murderous spree been carrying guns, the horrific rampage may well have been stopped much sooner.
If the police crossing Westminster Bridge on their way back from a commendation ceremony had had weapons, they could have halted the attacker in his tracks, if not impeded his progress towards Parliament.
Likewise, had Constable Keith Palmer, who Masood fatally stabbed, been armed, he would have been better able to defend himself. He may even be still alive, and the terrorist would not have got as far to the building.
Many of Constable Palmer’s colleagues helping to guard the Palace of Westminster are unarmed too.
In addition, it appears that Masood was shot dead not by armed officers based on site but a protection officer for Defence Secretary Michael Fallon, who just happened to be nearby because the minister had arrived for a Commons vote.
Normally, that entrance to Westminster is protected by just unarmed police.
They are only routinely supported by armed colleagues when the Prime Minister is expected in her motorcade.
Mark Rowley, the Metropolitan Police’s head of counter-terrorism, has described Parliament’s security arrangements as “proportionate”.
It’s true that there are plenty of police with guns around Parliament - but what we now know about the attack demonstrates that where there is the need for police, there is a need for arms.
Crucially, it was too easy the terrorist to get as far as he did, because Parliament is both an open set of courtyards and a warren of corridors to hide in.
Had there been more than one attacker, or had Masood been armed with a gun, it could have been much worse.
The most practical improvement to security in general is to have lots more police officers with guns, wherever they are.
We don’t know where the next attack will come, but having all police officers across the UK armed at all times would make them better placed to deal with the new terror threat.
This is as relevant to Scotland as it is to London and other major English cities.
After all, in what had previously been unthinkable, Glasgow Airport’s passenger terminal was the target of a botched terror attack ten years ago in June.
If there is another assault north of the Border, we should not rely on having another John Smeaton on hand to set about the assailant before armed police reach the scene.
Where Police Scotland went wrong over the more recent controversy with armed patrols was for the then chief constable to have sanctioned them unilaterally with no debate.
We will have to accept what some thought incongruous may have to become the new normality.