Concerns have been raised as Health Secretary Jeremy Hunt launched an investigation into the NHS breast screening programme.

This decision was taken after it came to light that hundreds of thousands of women in England were not invited for their screenings.

Below are some of the key questions and answers that residents might be looking for following the revelations.

What is the scale of the issue?

Since 2009, it is estimated 450,000 women in England were not invited for a screen and 309,000 women were not invited for a screen and are alive today.

Mr Hunt MP said it is not known whether any delay in diagnosis resulted in avoidable death, but it is estimated that between 135 and 270 women had their lives shortened as a result.

How do you find out if you missed out on a screening?

Public Health England says they have launched plans to attempt to make contact with all the women who missed out on screening invitations before the end of May. The first batch of letters - 65,000 - are due to be sent out this week. Women can seek advice by calling the helpline on 0800 169 2692.

When will re-screenings be carried out?

The agency says they anticipate that the screenings for those affected by the error will be completed by October 2018. Extra capacity options are being identified to avoid impacting on routine screening.

Who is entitled to the re-screenings?

All women that were not sent an invitation for their final screen will be given the opportunity for a new screening appointment. All women under 72 years old who are affected will receive an appointment letter informing them of their time and date. Women aged 72 years old and above will be able to contact a dedicated helpline to discuss whether a screen could benefit them.

What is being done to look into how this happened?

Health Secretary Jeremy Hunt has commissioned an independent review of the NHS breast screening programme to look at issues, including its processes, IT systems and further changes and improvements that can be made to the system to minimise the risk of any repetition of this incident.

Who will be involved with the review and how long will it take?

It will be chaired by Lynda Thomas, chief executive of Macmillan Cancer Support, and Professor Martin Gore, consultant medical oncologist and professor of cancer medicine at The Royal Marsden. A report is expected in six months time.

How was the error discovered?

The problem, which was caused by a "computer algorithm failure" dating back to 2009, was identified in January 2018 while reviewing the progress of the age extension research trial, AgeX, which is led by Oxford University. The ongoing study is reliably assessing the risks and benefits of offering an extra screen to women aged 71 to 73 and between 47 to 49 years.

Public Health England says it became apparent that a similar impact has resulted from long term problems with the routine programme as well. In addition, some local services have not invited everyone for a final screen in the 3 years before their 71st birthday.

The agency has carried out a thorough investigation including a detailed analysis of data going back to 2009 and has been advised by experts and clinicians. The fault has now been identified and fixed.

What is the NHS breast screening programme?

The scheme invites more than 2.5million women every year for a test, with women between the ages of 50 to 70 receiving a screen every three years up to their 71st birthday. Around two million women take up the offer.

There are 79 local NHS breast screening services across the country, with the number of women invited per screening service ranging from 25,738 to 254,645. Dorset's screen operation is managed by Poole Hospital NHS Foundation Trust.

How successful is the programme in cancer detection?

Public Health England says the programme detects around 18,400 cancers per year, saving 1,300 lives.