Temperatures were raised recently when Ben Bradshaw, the health minister, accused GPs of operating gentlemen's agreements not to poach each other's patients. This, he said, restricted patients' freedom to choose. The British Medical Association immediately dismissed the accusations as “nonsense”.

Why so defensive? Because it's true, that's why. When politicians misrepresent us as overpaid halfwits, who spend every afternoon on the golf course, it's water off a duck's back. Get as close to the truth as he did and the feathers fly.

Patients have always had the right to choose their GP and we have always had the right to choose our patients. Usually neither party exercises that choice.

If you move into my practice area, then you're my problem. I'm not going to hunt you down as soon as the removal van pulls away, but if you come to my surgery with proof of your new address, you're in. If you decide that you prefer Dr Lockupshop's single-handed practice down the road, no hard feelings.

Like Heathrow's runways my surgery runs at something like 99 per cent capacity. To make room for you, the family that used to live in your new home will be removed from my list of patients. When they moved off, they also moved on.

This one-in one-out system works tolerably well. For every heartsink with his or her 40-page internet printout from miraclecure.com that leaves the area another arrives preserving the delicate balance of the mumbo-jumbo yin-yang.

But long and bitter experience has taught me to tread carefully when anybody shows up asking to change doctor without moving house. Most of the GPs who work near me are capable and caring, and if one of their patients wants to jump ship my first instinct is to ask them why.

More often than not it's because their current GP won't play ball. They won't order a test the patient wants or prescribe a drug the patient needs. They won't fill in an insurance claim form or issue a doctor's note. Almost every time I've fallen for a sob story like that a few minutes spent reading the medical record has convinced me that the test wasn't needed, the drug wouldn't work, the insurance form was a scam or the patient was fit for work.

So it's no surprise that many GPs interview patients before agreeing to accept them, a process that starts as soon as they arrive at the reception desk.

My staff are trained to hit the panic button that drops the bulletproof shutters as soon as they hear the words: “My old GP was rubbish.” The only exception is for patients attempting to escape from the tiny minority of local GPs who are, admittedly, pants.

Professional etiquette forbids us from looking at their deranged prescription charts and laughing out loud, unlike the dentist whose first words to me were: “Did you put these fillings in yourself then?”

There are only two things that you can say to your new GP that will worry him more than the “My old Doc was rubbish” line. One is: “My old GP was brilliant!” This could mean that he was superb, able to leap tall diagnostic buildings at a single bound. More likely he was a rollover who agreed to every crazy request his patients came up with in a desperate effort to be loved and get home before midnight.

Either way I'm shafted. I'm never going to match up to the former and I'm never going to be able to undo the damage done by the latter.

The other opening gambit from hell might surprise you: “My husband/wife/child is a doctor.” Not because we're worried about unwanted second opinions, it's because Dr Murphy's Law of Ironic Medicine and Unforeseeable Complications ensures that whatever can possibly go wrong for that patient, will.

And they'll probably end up wanting to change their GP.

Dr Copperfield is a GP in Essex. He also writes for Pulse magazine and pulsetoday.co.uk

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