Britain is a sick society. One reason why sceptics doubt the current unemployment statistics is the fact that they exclude so many people who are ill in one way or another. And the number of individuals who seem to be very ill is at record levels. Nearly six million people are claiming to be sick.

Can we really be as unhealthy as the numbers suggest, or is something else going on? Despite efforts by the government to reduce the number of people claiming invalidity benefit - something you get if you are ill for a long time - there is still, apparently, underlying growth in this type of sickness.

If the nation's health continues to deteriorate in this way there will be serious repercussions, not least for spending on healthcare, but also on many other areas. Latest data suggest we are spending close to £7 billion (€10 billion) a year on invalidity benefit alone, money that a cash-strapped chancellor would dearly love to get his hands on.

Many people are profoundly dubious about the underlying merit of many of the claims for invalidity benefit, particularly as the system exists in large part to compensate people who have been injured at work.

Given that the nature of work in Britain has altered profoundly in recent decades - fewer and fewer of us work in dangerous, dirty or physically demanding roles - there is a great deal of suspicion about the underlying merit of many of the sickness claims. While this suspicion is undoubtedly unfair on the people who are genuinely ill, the sceptics' case has been reinforced by a study published towards the end of last year in the British Medical Journal.

While abuse of the sick pay system is the fault of the people who fraudulently claim the benefits, the finger of suspicion has long been pointed at parts of the medical profession. Some doctors, it is argued, collaborate in the abuse by too readily agreeing to sign people off work, either for a day or two or for much longer.

According to this line of reasoning, it is all too easy to wander in to a doctor's surgery and ask for a sick note of any duration. Saying no, apparently, is not part of medical training.

This caricature of medical practice has been around for a long time. And, like the description of people on long-term sickness benefits as chronic malingerers, it is a gross slur. But, like a lot of big and clever lies, it does contain a kernel of truth.

When we look at some of the worst unemployment black spots, it stretches the credulity of even the most liberal commentator to accept that three generations of the same household are suffering from chronic back pain. Grandfathers who were genuinely injured in industrial accidents, particularly in mines, seem to have passed on their illnesses to their sons and grandsons, even in areas where those mines have not existed for decades.

Researchers have looked at the behaviour of a group of Scottish general practitioners and found that doctors resent their role as "gatekeepers" for the benefit system. The report concluded that there "appears to be important deliberate misuse of the system by general practitioners". Doctors, it seems, are unable or unwilling to act as an effect filter of those who merely claim to be sick and those who genuinely are ill.

Comments like "I've no discrimination at all. If a patient says they want a certificate for three weeks for a cold, I give them one. No questions asked", were found to be typical (although by no means universal: some GPs refused to be bullied).

How worried should we be and what actions should be taken? It is clear that it is wrong (and very ineffective) to ask doctors to act as the benefit system's bouncer. Somebody else, somebody much nastier, has to do that.

But it is true, and always has been, that any system involving free money will ultimately be abused. The extent of the abuse depends critically on the design of the system. The most abused benefit system in history has been the Common Agricultural Policy, which looks like a deliberate effort designed to allow systemic fraud.

The abuse of welfare systems looks small beer in comparison. But not all welfare systems should be abolished (like the CAP). Some just need better design. Civilised societies must accept that welfare systems will be taken advantage of: but there is always scope for removing some of the more obvious abuses.