Privacy campaigners have accused NHS officials of trampling over rules protecting patient confidentiality after they demanded details of millions of GP appointments.
Dates, times and lengths of appointments made with family doctors in England as well as reasons for consultations, partial postcodes and dates of birth have been requested, according to a letter seen by the Daily Mail.
Appointment booking service EMIS was asked to hand over the information urgently by NHS official Tracey Grainger to allow demand for a seven-day health service to be assessed, it said.
NHS England insisted the data requested was not confidential or sensitive but declined to say what information was involved.
Campaigners raised fears about the prospect of patients being identified from the records and claimed the NHS "thinks it is above the law".
Phil Booth, coordinator of patient confidentiality campaign medConfidential, said he believed the plan breached the Data Protection Act.
He said: "With this single letter NHS England has shown it will put political motivations ahead of patient confidence.
"It evidently thinks it is above the law when it comes to protections for our patients' data.
"Their clear intention here is to route around doctors and patients, trample on every rule of confidentiality and collect it all."
Renate Samson, chief executive of Big Brother Watch, said: "This is not the first time NHS England have attempted to gather personal information on patients without their knowledge or permission.
"It is one thing to access basic data, such as how many appointments a surgery makes in order to plan services, but accessing data which includes the reason for the appointment with a date of birth and part of a postcode is quite another.
"At that point a patient could feel concerned that private identifiable medical information is being shared with people other than their GP. This does not enhance trust between doctor and patient.
"People are aware that their data is gathered, but they should be told if the data will be shared, and be given the option to say no."