What steps will be taken to prevent this happening again?
Since 2009 about 45,000 women aged between 68 and 71 have not been sent invitations for routine breast cancer screening in line with recommendations.
Health secretary Jeremy Hunt has said this could have led to 135-270 premature deaths and added that the failure to issue invitations was caused by a computer error.
Breast screening in England is managed by Public Health England (PHE) and is offered to women aged between 50 and 70 who are registered with a GP. Around 2m women are screened every year.
PHE is now contacting women affected by the blunder to offer them screening options and to say the issue has now been rectified and that the same failure will not be repeated.
Head of PHE Duncan Selbie has issued an apology, but patient groups have called for him to resign.
Jeremy Hunt said that irrespective of when the incident started ‘the fact is for many years oversight of our screening programme has not been good enough’.
Professor of the Public Understanding of Risk, Sir David Speigelhalter, said screening comes with harms as well as benefits.
He estimates up to 800 women may have been saved from harm by not being invited for their final screening because of the risk of over-diagnosis, which is more likely in older women.
According to Cancer Research UK for every 1000 women who take part in the UK screening programme, five will have their life saved, but 17 will be unnecessarily treated for a harmless cancer that would not have caused symptoms.
Cancer Research UK (CRUK): Breast screening error: women need reassurance, not misleading statistics