With almost unfailing accuracy, the Benefits Agency seems to target my most deserving patients, first to torment them with a series of medical examinations, then to deprive them of the cold comforts of state charity. Yet it leaves the more obviously fraudulent claimants among my patients severely alone to enjoy their ill-gotten gains in peace and perpetuity.

My first experience of these misjudgements is now more than a decade old. A patient who was dying of a slowly progressive and invariably fatal condition was deprived of his Disability Living Allowance (or whatever it was called then, for the terminology keeps changing, a change of name being the nearest we can get to improvement) not long before his death. I wrote to the office that had made this decision. Did it claim that he didn't have the condition from which he had been diagnosed as suffering? Did it claim that he was recovering from it - in which case I suggested a report in the Lancet? Did it claim that he wasn't getting better, but should not have been given the allowance in the first place?

A struggle ensued, involving his wife and children, GPs, a local MP, neighbours as witnesses, the Citizens Advice Bureau, a lawyer or two and more than one hospital consultant (to say nothing of the staff in medical records, secretaries and so forth). The allowance was restored shortly before his death, allowing him to die a happy man. Was this an example of the Benefits Agency's superior wisdom, giving him a purpose in his last months and allowing him to die in the odour of victory? Other interpretations are possible.

The latest example of the genre is a patient who suffered so badly from arthritis (with objective evidence of severe pathology) that he was sacked for not being able to do his job properly, an inability to which he freely confesses. He is also going blind. But the Benefits Agency says that he is not disabled enough to receive any additional benefits. Moreover, he is treated as if he were a criminal even for trying to obtain a little extra cash. Surely, he knew in advance that he was not entitled to it under the rules? Just as the god of amphibians is an amphibian, so bureaucrats assume that everyone is a bureaucrat.

Meanwhile, scores of my patients get a little extra money for being drunks or drug addicts. They can't work, because they are drunk all the time. So they get a perpetual allowance that - surprise, surprise - they spend on drink. I know that most of the money returns to the Exchequer, so it costs the taxpayer little, but it still seems perverse to me.

Actually, the number of people not working doesn't change nearly as much as is sometimes claimed. What changes is the ratio of sick to unemployed, currently at an all-time high of about 2.5 to 1. As we get healthier, so we get sicker. Here is a conversation I have had many times: [Me to patient] "What work do you do?" [Patient to me] "I don't work." "Why not?" "I'm on the sick." "What sickness do you have?" "I get a sick note." "Yes, but why?" "Because I'm on the sick."

The reasoning at the Benefits Agency seems to be this: most people who claim to be ill are not ill; therefore most people who really are ill are faking it. This is what is known as a good compromise.