A SON came to walk his father home after a stay in hospital for a minor operation. They set out down the road. Rain came on. They went back inside the hospital to shelter from the downpour. Result? A pounds 400 bill for the man's medical insurer for an extra day's hospital stay.

An insurance company policyholder had a breast-reduction operation because the weight of her breasts was giving her backache. She did not check first with her insurer to check she was covered. The insurer reduced the claim on the grounds that cosmetic surgery was not covered, and there was no proof that the operation had been done for a medical reason.

More and more people are taking out private medical insurance - 7 million of us have cover at present, and there could be 18 million by the end of the century. Since it is becoming more common and because of the astronomical sums of money which may be involved, the consumer aspects of private health care are coming more and more into public focus.

Private health care has traditionally been discreet, not to say secretive, and is not subject to consumer regulation. Julian Stain ton, managing director of Western Provident Association, is outspoken on the subject. 'You have more consumer protection buying a British Rail sandwich - at least BR have to show a tariff,' he says.

Hospital bills do not have to be itemised, though more and more are because, says David Cavers, MD of Norwich Union Health care, they are aware of a 'presentational problem' - it looks bad when the press reports cases of pounds 100 being charged for a tin of talc. Hospital accommodation, which makes up around 60 per cent of the total bill, has been forced down in the last year or so by insurers, who in turn are under pressure to keep costs, and hence premiums, as low as possible. The reduction in room costs causes hospitals to make up in other areas, hence sometimes ludicrous overcharging on single items.

Though insurers proudly tell customers that the bill is sent direct from the hospital to the company for settlement, Mr Stainton advises that the patient should check it to be sure it corresponds to the treatment received. A popular abuse is the one which caught out the man who took shelter from the rain - hospitals will add a full day's charge to the bill if you sit on for an extra 10 minutes waiting for a taxi.

Another favourite is 'insurance job syndrome', where costs are piled on in the knowledge that the insurer is paying. Hospitals will offer reductions where they think a patient is paying his or her own bills - you should check on price before you are admitted and, if appropriate, negotiate.

Improvements in consumer controls are not even being talked of at the moment but as the medical insurance market expands, progress in this area can also be expected.