Terminally-ill patients would be well advised to find out the religious beliefs of their doctor, according to research showing the effect of faith on a doctor's willingness to make decisions that could hasten death.

Doctors who are atheist or agnostic are twice as likely to take decisions that might shorten the life of somebody who is terminally ill as doctors who are deeply religious – and doctors with strong religious convictions are less likely even to discuss such decisions with the patient, according to Professor Clive Seale, from the centre for health sciences at Barts and the London school of medicine and dentistry.

"If I were a patient facing end of life care, I would want to know what my doctor's views were on religious matters – whether they are non-religious or religious and whether the doctor felt that would influence them in the kinds of decisions they were looking at," said Seale.

A patient who wanted their life prolonged at all costs in the event of a terminal illness, or did not want it prolonged, should make sure they had a doctor who was in sympathy with this.

Doctors are influenced by their beliefs, just as other people are, said Seale.

"It is easy for clinicians to present themselves as neutral appliers of science, but values do come into it," he said. That is accepted in abortion care, but the issue has not yet been widely discussed in the care of the dying. "I had a GP who was powerfully committed to not legalising euthanasia," said Seale. He has now changed his GP.

Seale's study, published online today in the Journal of Medical Ethics, was based on a survey of doctors in specialisms likely to care for people at the end of life, such as neurology, elderly and palliative care but also general practice. More than 8,500 doctors were contacted and almost 4,000 responded.

The doctors were asked about the care of their last patient who died, if relevant – including whether they had provided continuous deep sedation until death and whether they had discussed decisions judged likely to shorten life with the patient.

They were also asked their religious beliefs, ethnicity, and their views on assisted dying/euthanasia. More than 3,000 described the death of a patient.

Specialists in the care of the elderly were somewhat more likely to be Hindu or Muslim, while palliative care doctors were somewhat more likely than other doctors to be Christian, white, and agree that they were "religious."

The chances of a doctor making an ethically controversial decision expected or partly intended to end life was largely unrelated to the doctor's ethnicity, but was strongly related to his or her specialisation. Specialised doctors in hospitals were almost 10 times as likely to report this than palliative care specialists.

But regardless of their speciality, doctors who described themselves as "extremely" or "very non-religious" were almost twice as likely to report having taken these kinds of decisions as those with a religious belief.

The most religious doctors were significantly less likely than other doctors to have discussed options at the end of life with their patient.