She is dying of ovarian cancer but Bernadette Clements-Jewery is determined to use her remaining time well. Through her own terrible experience, she would like to alert people to the fact that expensive private health checks may not be as safe and reliable as they seem.

In May, worried about some uncomfortable symptoms, Bernie, 49, a nurse, went for a Bupa health check. She thought that by going privately and paying £400, it was less risky than relying on an overstretched NHS.

Yet two months after the test had given her the all-clear, she discovered that she had cancer and that it was at an advanced stage. She had to undergo major surgery and had her ovaries, uterus, cervix and fallopian tubes removed. But it was too late to save her and the chemotherapy she is now receiving will not be a cure.

Bupa has denied that the family doctor it used should have spotted the tumours and argues that ovarian cancer is difficult to detect. But one of Britain's gynaecological cancer specialists, Professor John Shepherd, has studied Bernadette's case and concluded that a proper check should have uncovered such extensive disease.

Her case is likely to raise concerns about the reliability of the expensive 'health MoTs', which are heavily marketed by the private medical insurance companies, netting the industry more than £31 million a year.

Hundreds of thousands of screenings are carried out each year, but there has been no systematic audit to show their effectiveness at detecting illnesses.

The Department of Health has been told about the case, but cannot intervene because the government regulates only private hospitals and clinics, not one-off tests.

Ministers set up the new National Care Standards Commission to regulate the independent sector, but this will not cover NHS doctors who work occasionally for the private sector - a loophole that the National Consumer Council has described as a 'grave oversight'.

Even if the system is changed, it will not happen in time to help Bernie and she does not want to take legal action.

'It's too late for me, I've got a death sentence,' she said, looking out of the window in her Kent cottage. 'But if one other woman is warned and goes elsewhere to get better advice and attention, then it's worthwhile.'

When she decided to go to Bupa in May, she thought she would be avoiding the perils of the NHS. A normally active woman, she had been feeling unwell for weeks - her symptoms included tiredness, weight gain, indigestion and bloating - and just wanted some peace of mind.

The test, at the Bupa St Saviours Hospital in Hythe, Kent, seemed comprehensive, including everything from sight and hearing tests to a mammogram and cervical smear. The report arrived a couple of weeks later, showing the mammogram and smear were clear. 'Nothing else was picked up so I thought my symptoms must be menopausal,' she said.

But by July she was feeling no better and this time her GP carried out an internal examination, after which Bernie was referred for a scan. This showed a large mass in the pelvis that was almost certainly malignant. 'I didn't cry until I was in the car on the way home,' she says. 'Once I saw the size of the thing on the scan I knew I was in trouble.'

By the end of July, she was admitted to the NHS Maidstone Hospital, for a major surgical procedure in which her ovaries, uterus, cervix, and fallopian tubes were removed. But her cancer had not been caught in time and had spread into the rest of her body, including the lymph and blood vessels. She has now started chemotherapy but realises the prognosis is not good.

'I'm buying myself a bit more time with the chemo but my chances of beating this thing are pitiful because I already have secondaries,' she says. 'Losing those two months may have made the difference between whether or not I survive.'

Having a family history of cancer is also a significant risk factor. Bernie's mother survived breast cancer after a mastectomy in her forties; her sister died of the disease at 48.

The local GP, who had been hired by Bupa to do the check, had this information, but Bernie feels he could not have taken it into account.

Horrified at the two wasted months, Bernie wanted to know whether an earlier diagnosis could have made a dif ference. Shepherd, of the Royal Marsden Hospital, studied her case and confirmed that in his opinion her tumours would have been present six to nine months before they were discovered in July, and that a careful pelvic and internal examination should have picked them up. He also pointed out that her symptoms in May were indicative of ovarian cancer.

But Bupa Wellness, the part of the company that carries out 70,000 health assessments a year, has denied the check was flawed, although it has refunded her the £400 cost of her screening. The company says it takes all complaints seriously and has investigated the case.

Dr Peter Mace, assistant medical director of Bupa Wellness, said the doctor carried out full internal and rectal examinations - something Bernardette denies. Dr Mace is adamant that the correct procedures were followed.

'It is not always that easy to feel things unless you have an idea of what you are looking for. That gets much harder if there is an abdominal tenderness, as there was in this case.

'Ovarian cancer is notoriously difficult to diagnose, which almost invariably presents late, with non-specific symptoms.'

For Bernie, these words fall far short of the apology she wants. 'They come out with platitudes like "We're sorry you're sick", but I want them to be honest enough to say that they made a mistake, and that they'll improve their procedures so what has happened to me doesn't happen to some other poor woman.'