The women were not sent a 'reminder' letter urging them to arrange a second smear test because the first test had either shown an abnormal result or one which the laboratory had been unable to read properly.
Health officials from the Merton, Sutton and Wandsworth Family Health Services Authority in south-west London admitted yesterday that some of the women may have developed pre-cancerous changes of the cervix which needed immediate treatment.
However, Dr Hilary Stirland, director of public health, said the risk of any of the women developing invasive cancer was 'very, very small'.
There are an estimated 3,860 women involved, aged between 20 and 64, attending 128 GP practices. Some of them last had a smear in 1988.
The failure of the follow-up system means that although the women and their GPs will have been told of the initial result by the laboratory, there is no record of whether or not they had another test.
Hundreds of women are known to ignore letters about tests and the 'reminder' letter is a safeguard for the national screening programme.
The latest blunder comes a week after the Chief Medical Officer, Dr Kenneth Calman, announced an overhaul of the national screening programme in an attempt to restore public confidence in it.
Failures in the screening programme in Liverpool, Oxford, Birmingham, and Strathclyde have highlighted problems at every level, from the taking of cervical smears to reading the results.
John Speirs, chairman of the authority, said yesterday that the problem was identified just two weeks ago, when it became clear that a standard 'reminder' letter for women in two categories - mildly abnormal or inadequate first tests - had not been included on the computer system.
As a result, the authority had no record that 1,865 women who had an inadequate test, and 3,085 women with a mildly abnormal smear, had been followed-up.
A total of 3,860 women have been identified who should visit their GP or community clinic for further investigation or a follow-up smear if required, Mr Speirs said. They would receive letters to that effect this week. Another 1,090 women have either had a smear or no longer require one.
The manager responsible is no longer with the authority. Mr Speirs said that he would resign if any serious clinical problems resulted from the blunder.
Mr Speirs said: 'I deeply regret what has happened and I am determined that we should give a full explanation of the mistakes that were made. I am also determined that we should learn lessons for the future to ensure that such mistakes are not made again.'
The problems in Merton, Sutton and Wandsworth appear not to be of the same order as previous smear test blunders, but have highlighted concerns about screening and the problem of getting women to have smears, even after they have been notified of abnormal results.
Dawn Primarolo, Labour health spokeswoman, said: 'It is a disgrace that women have once again been put at risk by this administrative blunder, despite ever increasing numbers of managers in the NHS who, Virginia Bottomley tells us, are there to improve efficiency.'
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