The failure to publish guidance on how A&E performance data is collected "continues to undermine the public confidence" in NHS statistics, an official watchdog has said.
Earlier this year, NHS England was accused of presenting its data in a way which could "mislead" the public after some hospital trusts appeared to have improved their waiting times when they had not.
In a letter to Mark Svenson, head of profession for statistics at NHS England, Ed Humpherson, director general for regulation at the UK Statistics Authority, said he was currently"disappointed" at the progress that has been made.
Referring to previous assurances from NHS Improvement, Mr Humpherson said: "I am therefore disappointed that A&E data collection guidance, based on agreed principles, has still not been published.
"This uncertainty continues to undermine the public confidence in the official statistics compiled from that data [A&E Attendances and Emergency Admissions].
"Resolving this uncertainty would be the best way for you to meet the needs of external users, particularly to demonstrate the trustworthiness of your statistics and to ensure you are transparent about future plans for these statistics."
Mr Humpherson said that in order to "help rebuild public confidence", the authority expects NHS England to publish an explanation of the issues and planned next steps.
Any revisions to the published statistics should also be presented in an easily accessible way, he added.
Sustained pressure on A&E departments over the winter saw the worst waiting time performances since records began.
Just 84.6% of patients were seen within four hours in March, falling to 76.4% at major A&E departments.
Hospitals aim to see, treat, admit, transfer or discharge 95% of patients within four hours of them arriving at A&E, but that target has not been met since July 2015.
The number of cases where patients waited over four hours to be given a bed on a ward after a decision to admit was made, known as "trolley waits", also rose from 198,000 last winter to 221,000.
Dr Nick Scriven, president of the Society for Acute Medicine, said: "We really need to have accurate data on how our systems are performing and to hear that these recommendations have not been implemented is distressing.
"The cornerstone of any plans we can make for next winter hinge on having a realistic picture of how things actually are.
"There is also the matter of timely data and how this is disseminated to those who need to know [via NHS England weekly winter sitrep reports].
"This year the sitrep reporting period officially finished at the beginning of March. Since then we have had patchy monthly figures of limited detail but can we now even trust that?"