Health authorities in Fife, Forth Valley and Tayside have revealed that almost 20,000 women have been affected by the screening failure.

And officials have accepted they cannot be certain whether or not lives have been lost.

The problem developed with a computerised system which calls women aged between 20 and 60 for routine cervical smears.

BBC Scotland Health Correspondent Abeer Parkes reports

Women who failed to respond to three invitations for smears before 1994 were suspended from the system.

This meant they were not invited back for screening again - which is against national guidelines.

The immediate priority is to trace 500 women whose earlier smears showed abnormalities, to ensure these were followed up at the time.

The affair is another embarrassment for smear testing in the UK, following high-profile scandals such as that involving Kent and Canterbury Hospital in the early 1990s.

The health authorities affected have apologised to the women after the latest problem came to light.

Susan Deacon: "Seeking report"

Scottish Health Minister Susan Deacon has called for a review of procedures but stressed that the risks to the women concerned were minimal.

However, Doctor Malcolm McWhirter, of Forth Valley Health Board, said he could not guarantee that there had been no deaths as a result of the problem.

He said: "That could be possible. If a woman had missed some of the recalls that could have been possible, I will not deny that."

The three health boards stressed there has been no failure of the laboratory system or the practice of reading cervical smears.

They have emphasised that anyone who has had a smear in the past five years is not affected by the present situation.

Health Minister Susan Deacon: "This matter must be put in context"

Ms Deacon said the boards will now prepare a report, which will be made public, on how the discrepancy in the screening system arose.

She said: "The priority now is just under 500 women whose last smear result was abnormal and who may require follow-ups.

"An abnormal smear is not at all uncommon and does not mean that a woman has cancer.

"I would also like to stress that any woman who has had a smear in the last five years is not affected by this problem."

Dr McWhirter said its was very important that those women whose smears showed abnormalities had a follow-up, although they did not necessarily indicate cancer.

He said: "The boards would urge all women to respond to their smear invitations."

Risks are said to be "minimal"

Letters are to be sent to all the 19,000 women left off the list over the next four months.

It was emphasised today that no names had been lost, and efforts would be made to contact all the affected women, several thousand of whom are believed to have moved away from the health board areas.

The health boards will jointly produce a report on the screening failure - with an interim report available in October this year and a final report expected in March 2000.

Ms Deacon added: "This is not a national problem and it is not a current problem.

"In practice it means that in these areas, because of a problem with their recall system, women who did not attend for a smear following an invitation and two reminders before 1994 were not invited again.

"That is something which should not have happened and would not happen today."