Look alike pharmacy packaging provided has caused further confusion for the patient or carer to identify and distinguish them from others, the NPSA found.
It has now emerged that Sir Liam will present preliminary figures to the NPSA conference but will add a "health warning" about what conclusions can be drawn.
The Evening Standard newspaper had claimed the findings were due to be published on Tuesday at a NPSA conference but Mr Milburn had suppressed them because of fears of how the public would react to the news.
"The NPSA is also setting up a Patient Safety Observatory which will draw together patient safety information from different sources, including the NRLS and studies such as this one from Dr Foster, to maximise our understanding and direct our safety solutions work, " she said.