Most people don't know that the NHS has a list of "never events", being a list of preventable events that should never happen.  The October 2012 Never Events Policy Framework defines never events as "serious, largely preventable patient safety incidents that should not occur if the available preventative measures have been implemented by healthcare providers".  The Framework contains a list of 25 never events.  These range from wrong site surgery, retained foreign objects post surgery and misidentification of patients to entrapment in bed rails, misplaced naso or oro-gastric tubes and maternal death due to post partum haemorrhage following elective caesarian section.  

There has been coverage in the news this week following the disclosure that there have been 750 such incidents reported in the NHS in the last four years.  The BBC website has produced an interactive table letting you explore the reported incidents by Trust:

http://www.bbc.co.uk/news/health-22466496

What is more interesting in many ways is the breakdown of the number of incidents by "event".  The October 2012 Framework makes very interesting reading, containing a table of the 2011/12 results.  Of the 326 incidents for that year (which seems remarkably high considering the overall statistic for four years), the overwhelmingly common category was retained foreign objects post operation, with 161 reported incidents.  Wrong site surgery followed with 70 cases, then 41 cases of wrong implant / prosthesis.  

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/127087/never-events-policy-framework-update-to-policy.pdf.pdf