The confidence of women in the cervical screening programme in the UK has already been undermined by a series of errors in the way labs have analysed smear tests.

The most serious previous problem happened in 1996 at Kent and Canterbury Hospital, where at least eight women died and 90,000 were recalled after screening errors led to the early signs of cancer in some tests being missed.

Other cases include:

• 1993 - 1,100 Birmingham women were recalled after a nurse took smears with a tongue depressor.
• 1994 - 4,000 women were recalled after a Merton, Sutton and Wandsworth Authority computer error meant abnormal results were missed.
• 1997 - 20,000 smear tests assessed at Inverclyde Royal Hospital in Greenock, Scotland, were reviewed after it was revealed some had been misread.
• 1997 - 8,000 tests from the James Paget Hospital in Gorleston, Norfolk, were rechecked after it emerged that lab workers were testing slides at home.
• 1998 - 1,000 women were recalled at St George's Hospital in south London after concern that some women with abnormalities were unsatisfactorily treated. This case is slightly different from the others in that it occurred after the initial screening process.

Major problem at Kent and Canterbury Hospital

According to a Department of Health report published in 1997, more than one in three laboratories where cervical smear tests are examined failed to meet national standards.

Eighty of the 181 laboratories had too many or too few "inadequate" smears, 34 were deemed to be too small to meet government efficiency targets and some were criticised for taking too long - up to nine weeks in some cases - to examine smears.

New standards

In an effort to improve standards, the former Chief Medical Officer Sir Kenneth Calman announced a series of measures. He wanted:

• Laboratories to apply for accreditation, with external examination, within six months.
• Consideration to be given to closing or merging labs examining fewer than 15,000 smears a year.
• Staff to be sent on refresher training.
• To create a "high level action team" to judge progress.

A subsequent report, published by the National Audit Office in 1998, found faults at every stage of the cervical screening programme. It also criticised the length of time women had to wait for their results.

Falling death rates

Nearly 4.5 million smears are examined by pathology laboratories each year. Despite the recent scare stories, the service is generally regarded as a major success.

Death rates for cervical cancer are falling

The programme is estimated to prevent up to 3,900 cases of cervical cancer a year. Death rates have also fallen dramatically over the last decade with about 40% fewer women dying from the disease compared with 1979.

Cervical screening is a method of detecting pre-cancerous changes in a woman's cervix, or the neck of the womb. It is the most common cancer among women in England under the age of 35 years.

Women are currently screened at least every five years from the age of 20 to 65.