Just looked it up on the NHS Direct website and found this:
The NHS Cervical Screening Programme in England offers free tests to women between the ages of 25 and 64.
Women who are registered with a GP are invited for screening tests based on a call and recall system. You should receive your first call for screening at 25. Unless any follow up tests are required, you will be recalled for screening after the appropriate interval. It is therefore important that you ensure your GP has your correct name and address details. You should inform them if these change.
In 2003, the NHS Cervical Screening Programme was changed so that women are offered screening at different intervals depending on their age. Research shows that this change will make the screening programme more effective. The new screening intervals are:
* Women should receive their first invitation for screening at 25.
* Women aged 25-49 are invited for screening every 3 years.
* Women aged 50-64 are invited for screening every 5 years.
* Women aged 65 or over are screened only if they have not been screened since age 50 or have had recent abnormal tests.
If you are unclear when your next screening test should be, or if you have any questions about the NHS Cervical Screening Programme, you should contact your GP or practice nurse.
Hope it helps more than my first, rather woolly answer!