Doctors' leaders are ramping up the pressure over controversial plans to share medical records, saying patients need to know how their data will be used outside the NHS.
Criticism of the care.data scheme is growing, with the British Medical Association (BMA) and the Royal College of GPs (RCGP) both warning in the last week that patients are being kept in the dark about the plans.
Today, the RCGP issued a further warning, saying it has written to NHS England requesting a six-point plan of action and "clarification" on what types of firms and organisations will be able to use the data.
RCGP honorary secretary, Professor Nigel Mathers said awareness of the scheme was low, and NHS England must show it has done "everything practically possible" to ensure patients know about their right to opt out.
The idea behind the scheme is to link data from GP records with information from hospitals to give an idea of what happens to patients at all stages.
The data being extracted from GP systems includes family history, vaccinations, referrals for treatment, diagnoses and information about prescriptions.
It will also include biological values such as a patient's blood pressure, body mass index and cholesterol levels.
Personal confidential data (PCD) identifiers will also be taken, such as date of birth, postcode, NHS number and gender.
The written notes a GP makes during a consultation will not be extracted. The data will be held by the NHS Health and Social Care Information Centre (HSCIC) and anonymised by officials there.
Fully anonymised data will then be made available publicly to anyone outside the NHS.
Data considered to be potentially identifiable - for example where a patient in a small town has a rare disease - will only be released to approved organisations for the specific purpose of benefiting the health and social care system.
NHS England plans to make this "amber" data available to organisations outside of the NHS, such as medical charities, think tanks, data analytics companies and universities.
Private firms such as pharmaceutical companies may also be able to obtain the data. Geraint Lewis, chief data officer of the NHS, has said officials believe it "would be wrong to exclude private companies simply on ideological grounds".
He said: "Instead, the test should be how the company wants to use the data to improve NHS care."
In its six-point plan, the RCGP said it wants to know how "amber" data will be disclosed, with " particular assurance that organisations outside the NHS will not be permitted to use such data for commercial purposes".
It also wants confirmation that data disclosed to third parties outside the NHS "will not be sold for profit, but instead be charged for on a cost-recovery basis only".
The RCGP wants to know who will take decisions on the disclosure of identifiable and potentially identifiable data, and the robust controls that will be put in place to manage its use.
The college is also calling for much more publicity of the scheme, including n ational TV, radio and online adverts highlighting the need for people to decide whether they wish to opt out.
A personalised letter should also be sent to everyone whose records could potentially be uploaded as a supplement to the general NHS England leaflet being sent to households.
In the letter, Prof Mathers said: "The RCGP believes that care.data has the potential to deliver enormous benefits for patients by helping the NHS to improve the quality of care it delivers.
"While we recognise the substantial programme of activity and materials that has already been developed to communicate care.data, we believe that there is a deficit of awareness and understanding regarding the scheme amongst many members of the public and professionals.
"If the roll out of care.data is to go ahead according to the current schedule, action is urgently needed to tackle this, and to ensure that there is absolute clarity about how the scheme will work.
"Crucially, where a scheme is based on an opt-out approach, such as in the case of care.data, we believe that it is vital that the NHS is able to show that it is beyond reproach in having done everything practically possible to ensure that patients and the public know about their right to opt out prior to it going ahead.
"At present, we are concerned that levels of awareness concerning care.data are very low, and believe that there is a strong case for substantial additional activity over and above that already in place to tackle this."
Two polls for the Medical Protection Society (MPS) published on Monday showed most patients have not yet received leaflets explaining the system and GPs fear patients will not be informed enough about opting out.
Of 1,400 members of the public, 67% have not received the leaflet from NHS England explaining the new system and 45% did not understand care.data from what they have read or heard.
A separate MPS survey of more than 600 GP members showed 80% felt they themselves did not have a good understanding of how patient data would be used.