On 11 March 2015, the Supreme Court handed down judgment in the case of Montgomery -v- Lanarkshire Health Board and has clarified the law in relation to consent.


The case concerned a child who was injured at birth as a result of shoulder dystocia and associated hypoxia. His mother was diabetic and the foetus was large for dates. She was not told about the risk of mechanical problems during delivery and neither was the possibility of an elective caesarean section discussed.

Of interest, it was the evidence of her obstetrician that ‘everyone’ in that situation would elect for a caesarean section if it were offered, but in her view this was not in the maternal interests.


The judgment can be summarised as follows:

  • An adult person of sound mind is entitled to decide which, if any, of the available forms of treatment to undergo, and consent must be obtained before treatment.
  • The doctor is under a duty to take reasonable care to ensure that the patient is aware of any material risk involved in any recommended treatment and of any reasonable alternative or variant treatment. 
  • The test of materiality is whether, in the circumstances a reasonable person in the patient’s position would be likely to attach significance to the risk, or the doctor is or should reasonably be aware that the particular patient would be likely to attach significance to it. 
  • The assessment of whether a risk is material cannot be reduced to percentages. Factors include the nature of the risk, the effect its occurrence would have on the life of the patient, the importance to the patient of the benefits from the treatment, the alternatives available and their risks. The assessment is fact-sensitive and specific to the characteristics of the patient. 
  • The doctors’ duty is not fulfilled simply by providing technical information which the patient cannot understand, or by routinely demanding a signature on a consent form.
  • There is a therapeutic exception, where disclosure of a particular matter would be detrimental to the health of a patient, but this is a very limited exception.


All medical personnel involved in consenting patients must become familiar with this decision.

It is important that consenting practices move quickly away from focusing on the percentage risk of occurrence and instead consider the materiality of the risk from the perspective of the patient.

Taking a single example from obstetric practice, it is difficult now to envisage a circumstance in which it will not be a legal obligation to offer an elective caesarean section to any mother with an elevated risk of shoulder dystocia.

Of course, the decision is not restricted to obstetrics and is relevant to all consent obtained in a medical context.