The mistake was revealed by Heath Secretary Jeremy Hunt today in the House of Commons, who said it has affected 450,000 women nationwide, 309,000 of whom are still alive.
The computer error - which dates back to 2009 - had meant 450,000 women aged between 68-71 were not invited to potentially life-saving breast cancer screening appointments.
Mr Hunt added that computer models indicate between 135 and 270 women may have had their lives shortened as a result.
Speaking today in the House of Commons, Health Secretary Jeremy Hunt apologised ‘wholeheartedly and unreservedly’ for the error on behalf of the government, the NHS and Public Health England.
He said: “Many families will be deeply disturbed by these revelations, not least because there will be some people who receive a letter having had a recent diagnosis of breast cancer.
“We must also recognise that there may be some who receive a letter having had a recent terminal diagnosis.
“For them and others it is incredibly upsetting to know that you did not receive an invitation for screening at the correct time and totally devastating to hear you may have lost or be about to lose a loved one because of administrative incompetence.”
The Heath Secretary said all women who were not sent an invitation for their screening would now be given the opportunity to have a new appointment.
Those under the age of 72 will receive an appointment letter informing them of the time and date, while those over 72 will also be offered a screening and have access to a helpline to decide if it will be beneficial.
The helpline number is 0800 1692692.