More than 1,100 patients have suffered from NHS "never events" - mistakes so serious they should never have happened - in the past four years.
Around 800 of these have either had the wrong area operated on or "foreign objects" such as gauzes, swabs, rubber gloves, scalpel blades or needles left inside them.
Some of the worst mistakes revealed by a Press Association investigation include:
- A woman having her fallopian tubes removed instead of her appendix
- A man having a testicle taken off instead of just the cyst on it
- One woman having a kidney removed instead of an ovary
- Another patient had a biopsy taken from their liver instead of their pancreas
- Operations were carried out on the wrong hips, legs, eyes and knees
- Blood transfusions with the wrong blood were given
- Feeding tubes were put into patients' lungs rather than their stomachs -which can prove fatal
- Diabetic patients were not given insulin
- Other patients were given the wrong type of implant or joint replacement
- Patients were mixed up with others
- Drug doses given out were far too high in some cases
Katherine Murphy, chief executive of the Patients Association, said: "It is a disgrace that such supposed 'never' incidents are still so prevalent.
"With all the systems and procedures that are in place within the NHS, how are such basic, avoidable mistakes still happening? There is clearly a lack of learning in the NHS.
"These 1,100 patients have been very badly let down by utter carelessness. It is especially unforgivable to operate on the wrong organ, and many such mistakes can never be rectified."
The analysis of data published by NHS England shows there were 254 never events from April 2015 to the end of December 2015.
From April 2014 to March 2015, there were 306 never events, and from April 2013 to March 2014, there were 338.
In the previous year - from April 2012 to March 2013 - there were 290.
In 2014/15 Colchester Hospital University NHS Foundation Trust was the worst hospital trust, with nine never events recorded.
Royal College of Surgeons president Clare Marx said: "While these cases are very rare, never should mean never.
"The NHS must continue to learn from these errors so we can become the safest healthcare system in the world."
An NHS England spokeswoman said: "One never event is too many and we mustn't underestimate the effect on the patients concerned.
"However there are 4.6 million hospital admissions that lead to surgical care each year and, despite stringent measures put in place, on rare occasions these incidents do occur.
"To better understand the reasons why, in 2013 we commissioned a taskforce to investigate, leading to a new set of national standards being published last year specifically to support doctors, nurses and hospitals to prevent these mistakes.
"Any organisation that reports a serious incident is also expected to conduct its own investigation so it can learn and take action to prevent similar incidents from being repeated."