A new body set up to help the NHS learn from mistakes will be "crippled" unless it is given a proper legal footing, MPs have warned.
The Healthcare Safety Investigation Branch (HSIB) needs its independence written into law, which would enable staff involved in making mistakes to have a "safe space" to talk about what went wrong, they said in a report.
The HSIB for England came into force last April with the aim of supporting and guiding hospitals on investigations and carrying out some investigations itself.
Health Secretary Jeremy Hunt said the creation of "safe spaces" for staff to speak about what went wrong without fear of repercussion would help bring new openness to the NHS.
But a new report from the Commons Public Administration and Constitutional Affairs Committee (PACAC) says primary legislation is needed to create these safe spaces and ensure the HSIB is independent.
MPs said they were deeply concerned that HSIB is being asked to begin operations without the necessary legislation in place.
The report also warned there is still much to do establish a joined-up culture of learning and investigation within the NHS.
PACAC chairman and Conservative MP, Bernard Jenkin, said: "There is an acute need for the Government to follow through on its commitment to turn the NHS in England into a learning organisation; an organisation where staff can feel safe to identify mistakes and incidents without fearing the finger of blame."
He said that without legislation, the ability of HSIB to "contribute to the development of a learning culture in the health system will be crippled", adding: "This is not acceptable."
The report also found that a culture of blame still exists within the NHS and, despite previous reports, "there is precious little evidence that the NHS in England is learning".
It added: "We found that, while a number of initiatives exist to improve the health service's investigative culture, there was also a distinct lack of co-ordination and accountability for how these initiatives might coalesce."
Commenting on the report, Parliamentary and Health Service Ombudsman Dame Julie Mellor said: "We know from our casework that families who complain to the NHS want lessons to be learned so that future mistakes are avoided.
"The NHS still has a long way to go to provide staff with the relevant skills to carry out fair, high-quality investigations into avoidable harm.
"The government and NHS leaders must commit to providing training, national standards and accountability for the NHS, to make it safer for all."
A Department of Health spokeswoman said: "We are committed to ensuring the NHS becomes an organisation that learns from its mistakes.
"That's why from April this year, all NHS Trusts will be required to publish how many deaths they could have avoided had care been better, along with the lessons that they have learned.
"The Healthcare Safety Investigation Branch will help the NHS learn from mistakes in the same way that the airline industry does.
"As the Health Secretary said last year, we completely agree that it should be as independent as possible which is why we are committed to pursuing legislation."