This was the week in which the mobile phone lived up to the opinion of Julia Carling and became an offensive weapon. A chap trying to make a one-2-one found himself spreadeagled in the road, one-to-five with a police rapid response unit toting Heckler and Koch semi-automatic guns.

Emerging from the Dorchester Hotel in London, the man was spotted by a less-than-sharp-eyed passer-by who mistook his phone for a gun in a holster under his jacket and reported him. Within seconds a Metropolitan Police rapid response unit was summoned, seized the supposed gunman and his friend, trussed them up and hauled them into a police van.

The only lucky person on the scene turned out to be a bystander who had brought his camera to capture London life, thought he was about to capture a London death, and shot a roll of film, sending it to the Evening Standard and ending up quids in.

With the rapidity of the police response thus proved, and the growing number of shortsighted people in London, from now on one will hesitate to wave a Mars bar or an over-ripe banana about in public. And anyone who fancies an ice-cream and says in public: "I'm just going to get a Magnum" can expect to be helping the police with their inquiries before the day is out.

Scenes like the one outside the Dorchester are of the sort that we tend to say are "just like America". But it could never happen there, say the New York police, and not just because your mobile phone would be nicked if you tried to use it on the street. American police would not stage such a response unless they believed there was imminent danger either to themselves or the public.

They are also becoming less trigger-happy generally, not least because of the following mind-boggling statistic: nearly half of all US policemen shot in the line of duty are victims of police weapons, very often their own. Join the NYPD, but don't whatever you do make yourself unpopular.

But back here, as the New Scotland Yard spokesman pleaded in so many words, what is a poor police officer to do? Or, as he officially put it, "When police are alerted to an armed incident we are duty bound to react accordingly, and armed units are automatically deployed."

Any 999 call claiming that someone was armed in a public place would be acted on in the same way, he added. Police would use their discretion when they took these calls, but if the circumstances seem suspicious "they have to throw caution to the wind and go for it".

All in all, better perhaps an innocent man rudely handled, shaken but not stirred, than a maniac on the loose. But to avoid passers-by thinking you have a holster, it might be wise to carry the mobile phone in the trouser pocket. Though that too might earn you suspicious glances.