Tougher guidance urging GPs to report patients who continue to drive when not medically fit has come into force.
New advice by the General Medical Council (GMC) states doctors have a duty to inform the authorities if a patient is driving against medical advice.
Doctors do not need a patient's consent to alert the Driver and Vehicle Licensing Agency (DVLA) - or Driver and Vehicle Agency (DVA) in Northern Ireland - when a patient has continued driving.
The strengthened advice, which came into effect on Tuesday, says GPs should "make every reasonable effort" to persuade a patient unfit to drive to stop, and then inform the authorities if they believe there is a "risk of death or serious harm" to others.
Doctors should attempt to inform a patient of their intention to disclose personal information before contacting the DVLA or DVA.
The guidance aims to help GPs balance their legal and ethical duties of confidentiality with wider public protection responsibilities.
Steve Gooding, director of motoring research charity the RAC Foundation, said drivers with certain serious medical conditions might fear losing their licence if they follow doctors' orders and inform the DVLA, but with the right treatment, many illnesses "will not lead to people having to hang up the keys".
He told the Press Association: "The worst thing people can do is ignore what they are told by their general practitioner, because if they don't inform the licensing body then - as this guidance makes clear - the GP should and will."
Gary Rae, campaigns director for road safety charity Brake, said: "We appreciate that having to give up driving because of a medical condition is a difficult step for some individuals, and this is a discussion that needs to take place with family, GPs and other medical professionals.
"I would appeal to all drivers to ensure that they declare any relevant medical conditions to the DVLA/DVA to help keep all road users safe."
Dr Barry Parker, an adviser at medical defence organisation MDDUS, said no doctor wants to act against their patient's wishes but "confidentiality cannot be absolute".
He went on: "There are situations where a doctor may have to disclose confidential information in order to protect the public interest, even when consent has been refused by the patient."
Motoring offences lawyer Julie Robertson warned she has dealt with cases where GPs have reported patients to the authorities without liaising with them first.
She said: "What I've seen in the past year is GPs circumventing the initial steps of the guidance - jumping straight to informing the DVLA, and without their patients' knowledge despite the fact that this is an absolute requirement.
"People trust their GP, and these sort of breaches erode a really important relationship."
AA president Edmund King said: "Rather than forcing older drivers to retake their tests or introducing tough medical tests across the board, we would prefer to see GPs take a more active role in telling their patients they are unfit to drive. It is best practice to tell the patient first before the DVLA.
"Research in the past found that the training of GPs on medical aspects of driving varied considerably depending on where that training was done. GPs and families of patients both have key roles in convincing drivers when they need to hang up their keys."