He told her that he was going to end his life by jumping in the canal. He was, incidentally, a non-swimmer.

She contacted the police. She could have rung the fire and rescue service; British Waterways; the boy's friends or family. No, she called the West Yorkshire Police, as do two million people each year.

Every one of those calls reveals a personal or general crisis, ranging from the banal – a cat up a tree – through the traumatic, like a motorway pile-up, to the downright dangerous such as a "man with a gun".

One of the most amazing things I find about policing, even after 35 years as a serving officer, is the British public's sheer breadth of expectation. I am also proud of just how often we meet that expectation, sometimes against all the odds.

Back to the call at issue. PCs Robert Dovey and Glenn Preer were on patrol in the Knottingley area when they received the message about the suicide threat.

They found the man on the parapet of a bridge over the Aire and Calder Canal. As they approached him, he jumped without warning and disappeared below the pitch-black water.

Let me pose a question to you. What would you do next? This is the type of dilemma that faces your fellow citizen, who just happens to wear police uniform, every shift.

PC Dovey, a decent swimmer, stripped and dived into the murky depths. Our would-be suicide victim popped up to the surface, thrashed about for a few seconds, then disappeared below again. PC Dovey dived to locate him and brought him back to the surface.

This was no mean feat. The man is six feet tall, weighed 14 stones and clearly didn't want to be saved. The officer struggled to get his subject to the bank where PC Preer, and colleagues, pulled him to safety.

There is absolutely no doubt that PC Dovey saved a life last Thursday. I am proud of him, and you may feel the same emotion.

But, in these days when health and safety regulations appear to have an elevated and authoritative status, how should I respond? The officer put his own life at risk. There are dozens of cases of water rescuers dragged down by panicking victims. To commend PC Dovey is to encourage others to follow his example. Who knows where that could end up?

Two years ago, the previous two Metropolitan Police Commissioners were literally "gripping the rail" at The Old Bailey because they were accused of not having done enough to prevent their officers pursuing suspects across rooftops.

A brave officer had fallen to his death. Similarly, the Chief Constable of Greater Manchester was accused of not having done enough to protect the health and wellbeing of DC Stephen Oake when he was killed by a terrorist that he, and other officers, were detaining.

I was asked by DC Oake's father to deliver a letter to the Health and Safety Executive, encouraging them not to continue with a prosecution.

His son, Stephen, was, he said, only doing the job that he loved.

The world is a little mad these days. The world, and the people who inhabit it, are not perfect. There is this organisation called the "police service" that is a service of first and last resort.

We in the service joined it because we wanted to be of assistance to people in a crisis. But the armchair perfection of the "health and safety Taliban" is intent on coming between us: creating doubt, where there was once certainty, over our mission; and demonstrating, post hoc, the chaos that surrounds all crises as evidence of a failure to plan and protect.

It is genuinely easier, in that kind of environment, to do nothing. We are not trained, equipped, practised or informed sufficiently for this or that particular scenario, so we'll stand back.

I have seen the anguish on the face of the mother, whose two daughters, Vicky Horgan, 27, and Emma Walton, 25,were shot a couple of years ago at a garden barbecue party at Highmoor Cross, Oxfordshire, as she asks why it took 20 minutes for the police and ambulance crews, who were parked a safe distance away, to attend the scene where her daughters lay dying.

I can tell you, as a police professional with some experience of firearms incidents, that it is the "health and safety zealots" who were responsible for that anguish.

I cannot write about health and safety without mentioning two matters in the news recently. The Police Community Support Officers who didn't jump into the lake in Manchester. They arrived at the scene 10 minutes after 10-year-old Jordon Lyon had last been seen on the surface of the water. He had, sadly, drowned. To jump in would have been symbolic, perhaps even heroic, but ultimately pointless. We teach all of our officers to weigh up risks before action.

Secondly, the Metropolitan Police conviction over the tragic shooting of Jean Charles de Menezes at Stockwell Tube Station. A triumph for health and safety, a lucrative new territory for lawyers, a disaster for common sense.

On every account, the Metropolitan Police were dealing with a complex, dynamic and dangerous set of circumstances. Four terrorists on the run two weeks after the 7/7 suicide bombings.

The Met has never been accused of intentional murder or even manslaughter through gross negligence. But did they do enough to protect life, which is the crux of the case?

The world, for goodness sake, is a dangerous place. We're just doing our best to respond to the risks and the dangers, and we won't always get it right.

And, on that last sentence, hangs the real dilemma for society in its sleep-walking acceptance of the health and safety mantra. Against the context of an imperfect world and an imperfect ability to control it, the police will not get things right every time.

If we are to be punished and pilloried when that happens, then it is rational to go no further than our job description – "To preserve the peace and prevent, as far as possible, offences against people and property".

It doesn't say anything in that declaration, taken on oath by every officer, about jumping in canals or running into burning buildings. There was no conception, when the declaration was first written, of tackling suicide bombers armed with deadly explosives.

If society wants a counsel of perfection, then it should expect a lot less at the margins.

I've done 35 years of pushing the boundaries and I'm not going to stop now. I'm going to commend PC Robert Dovey for risking his life last Thursday to save another.

I shall tell him that he acted in the finest traditions of West Yorkshire Police and, in so doing, I encourage his 10,000 colleagues to follow his example. It would be nice to know that this is what society wants from its police force.

You might understand if I am a little less certain in these times when health and safety appears to be king.

Sir Norman Bettison is Chief Constable of West Yorkshire Police.