Parliamentary and Health Service Ombudsman Julie Mellor said:
'When public services fail, it can have serious effects on us as individuals. We know that when people complain, they often want three simple things: an explanation of what went wrong, an apology and for the mistake not to be repeated.
'We know in other industries like aviation and construction when things go wrong they investigate to find the root cause, not to determine blame. They design and deliver services based on reducing or eliminating mistakes.
'Our casework indicates that there is a wide variation in the quality of NHS investigations into serious cases such as complaints about potential avoidable harm. These include failure to explain fully what happened and why, inadequate involvement of the complainant and a lack of independent clinical input.
'That's why we will examine our casework, including more than 250 cases of potential avoidable deaths. We will analyse whether an investigation would have been appropriate but did not take place or when an investigation took place but was not of a high enough standard.
'We will work with experts across health and other sectors to gather evidence of best practice and areas of improvements and will make recommendations for system wide change to the leadership and delivery of patient safety. We will publish our initial findings early next year.'