THE number of women suffering from ovarian cancer has increased by nearly 20 per cent over the last two decades in England and Wales, and almost a quarter in Scotland, cancer experts warned yesterday.

But five-year survival rates across the UK have remained ''worryingly low'' at less than 30 per cent, one of the lowest rates in Europe, the Cancer Research Campaign announced.

Ovarian cancer is the fourth most common cancer, and the fourth biggest killer cancer, in British women. And unlike many cancers, there seems to be a higher risk among relatively affluent patients.

Gateshead's Queen Elizabeth Hospital is one of 12 centres taking part in a ten year screening trial involving 200,000 post-menopausal women which could lead to the setting up of a national screening programme for ovarian cancer.

Just 29 per cent of UK women are still alive five years after diagnosis, compared with 45 per cent in Sweden and Austria and 41 per cent in Spain, the charity said. Only the poorer European countries of Slovakia and Estonia came out lower than the UK in the survival rate league table, with a rate of 26 per cent.

Says Professor Ian Jacobs, consultant gynaecological oncologist at St Bartholomew's Hospital in London: ''More than 14,000 British women are diagnosed with gynaecological cancers each year. Almost half of these are ovarian cancers and, sadly, because this cancer is often discovered late, the outlook for many ovarian cancer patients is poor.''

The reason for the rise in incidence is unclear, but researchers believe that lifestyle factors and fertility are important. The disease is commoner among white women, and in those from more affluent social groups.

Doctors know a woman's risk of the disease is reduced if she has had children, and decreases with each pregnancy. Using the combined oral contraceptive pill also reduces risk, by up to 80 per cent, in women who use it long-term, according to the Cancer Research Campaign.

Overall, there has been a decrease in the death rate from the disease, but an increase in actual numbers of women dying. This is a reflection of the growth in the population at risk, says the charity.

''We've already seen how screening for cervical cancer has made a tremendous impact on survival," says Prof Jacobs. "Thanks to this, and to improvements in surgery, radiotherapy and chemotherapy, UK mortality from cervical cancer has halved over the last 20 years. Now we want to see this improvement matched in ovarian cancer.''

Results from the Gateshead trial, which is by invitation only, could determine whether screening for ovarian cancer definitely saves lives.

Some of the women taking part in the trial will be screened annually, while others will be followed up without screening.

Women who are suitable for the trial, which is funded by the Medical Research Council, Cancer Research Campaign, Imperial Cancer Research Fund and the Department of Health, have been approached by the hospital.

The lifetime risk for a woman in England or Wales developing ovarian cancer is one in 48. Symptoms of the disease may include abdominal swelling, pain, nausea, bloating and weight loss. If caught early, when the disease is still confined to the ovaries, surgical treatment alone can provide a cure. But early diagnosis is difficult because symptoms are often vague and may be delayed until the disease is already widespread.

Professor Mike Richards, National Cancer Director, stresses: ''The Government has identified cancer as a top priority within health. The NHS Cancer Plan, published a year ago, recognised that the UK lagged behind many European countries in its cancer survival rates, including those for ovarian cancer. The Cancer Plan sets out a comprehensive strategy to tackle cancers and specific guidance has been published related to gynaecological cancers. Good progress is being made, but it will take time before this is reflected in five-year survival rates.''

The warning about ovarian cancer came as a new international clinical trial for ovarian cancer was being announced at the annual meeting of the British Gynaecological Cancer Society. The trial will begin in the New Year and will examine the use of different chemotherapy combinations in women with advanced ovarian cancer.

Dr T S Ganesan, Consultant Medical Oncologist at Imperial Cancer Research Fund and one of the UK clinicians managing the trial, says: ''The study will initially look at five different combinations of chemotherapy, but after the first stage, only the most promising treatments will continue to be examined. This will speed up our evaluation of the drug combinations and means we'll be able to deliver the best treatment to those who need it most more quickly. We hope to see initial results within three to four years.''

The trial is being co-ordinated in Europe by the Medical Research Council and patients will be entered from the UK and Italy.