The whole subject was considered at length by the House of Lords in Sidaway v. Board of Governors . In 1973, Mrs Sidaway underwent an operation to relieve the pressure on a nerve root that had been identified as the cause of her persistent pain in her arm and shoulder. The risk of the operation included a 2% risk of the nerve root damage and less than 1% risk of damage to the spinal cord.
Unfortunately Mrs Sidaway sustained damage to her spinal cord and sued on the grounds that she had not been warned of the risk of this type of injury. Mrs Sidaway's action failed because it was determined that a responsible body of medical opinion would not have warned her of these risks. The Law Lords, by a majority of 4 to 1 endorsed the rejection in Chatterton v. Gerson and Hills v. Potter of the applicability of the doctrine of informed consent in English law.
In fact informed consent is arguably highly practical to apply in that one would simply tell the patient all the risks associated with the proposed treatment. However, it could be further argued that in many instances this would overwhelm the patient to the point where he is not in a position to balance the information given and would not lead to consent being any more informed in that respect, a view supported in the same case by Lord Templeman. Reason
The reason behind the reluctance of the majority in Sidaway to embrace the doctrine of informed appears, by analysis of Lord Bridge's speech, to be two-fold; firstly the doctrine does not take full account of the variety of factors that influence a doctors clinical judgement, and secondly it is unrealistic to separate the primary medical problem from the issue of disclosure of information. However, this reasoning is open to criticism. The first reason given by Lord Bridge supports the paternalistic approach and, it could be argued, underestimates the doctors ability to close ranks.
The second reason supports the notion that giving information is part of the treatment and should not be judged separately and in so doing, arguably fosters the custom of deference to doctors. Following Sidaway the professional standard was given full support in Blyth v. Bloomsbury Health Authority and in Gold v. Haringey Health Authority. Nonetheless, it was agreed that the doctor is not obliged to tell the patient everything but he is similarly not entitled to decide everything.
Lord Scarman considered that a deciding factor would be whether a risk was material. The Materiality of Risk So what makes a risk material? It appears from the majority judgements in Sidaway that certain risks must be warned about. Lord Bridge considered that the court would consider negligent non-disclosure of a particular risk if it entailed: "….. substantial risk of grave adverse consequences" In Rogers v. Whittaker  W at the age of 9 had been rendered blind in her right eye.
Despite this she had gone on to live a normal life; she worked, was married with 4 children and enjoyed an extensive social life. 40 years after the operation she was advised by Dr Rogers, an ophthalmic surgeon, that there was an operation which could improve the cosmetic appearance and potentially the function of her right eye. W underwent the operation, but unfortunately a rare complication occurred which led to the loss of the vision in her left eye, once good eye.
In addition as the sight of her right eye had not been restored in any W was almost blind. There was no negligence in the performance of the operation and therefore the question turned on whether the failure to disclose the complication of sympathetic ophthalmic should have been disclosed. Interestingly in finding for W the court relied upon the decision in Canterbury v. Spence  insofar as they applied the reasonable patient test. However the court took a subjective approach to the test i. e. 'what did this patient want to know.
' Thus whilst the percentage probability risk occurring may assist in determining its magnitude, it does not determine whether it is 'special' to the patient by the sideway standard. Clear side What is clear is that a balance needs to be achieved. If one follows the argument supporting self-determination to its logical conclusion a patient denied information in relation to a risk (who then goes on to suffer that particular complication) will, it could be argued, always claim that the absence of that risk was an important factor when he have his consent.
Or to put it another way, had he been told of the risk he would never have agreed to the operation, irrespective of how remote that risk may have been. This was even recognised by Lord Scarman in Sidaway, who was the strongest supporter of fully informed consent In conclusion it is submitted that Sidaway gives us a 'modified professional cocktail mixed with a slice of patient autonomy and a twist of objectively'. In the more recent case of Pearce v. United Bristol Healthcare Trust, the Court of Appeal has moved into what has been described as "uncharted waters".
In deciding when a risk is significant, Lord Woolf MR confirmed that it is the duty of the doctor to warn a patient of a risk if the information is needed so that the patient can determine for him/herself what course he or she should adopt. Kennedy and Grubb Kennedy and Grubb argue that Lord Woolf is saying that the information does not have to be one which would have altered the patient's position, merely one that a reasonable patient would consider "relevant" as opposed to "determinative".
However the contrary could be argued, that in fact Lord Woolf is saying quite the opposite in that the information has to assume the elevated status of being "needed" and that it would "affect the judgement" which implies that it would be information capable of changing the patients decision. Of course the patient is in any event required to establish a casual link between non-disclosure and the injury incurred and therefore surely only information capable of being determinative would suffice. Conclusion
In conclusion, it has been determined that a doctrine of informed consent does not exist in English law, and has been considered in arguably the most important case on this matter as " … contrary to English law" (Sidaway). It is clear, however, that the law is moving away from a purely professional test and the law as it stands is therefore a combination of professional test, tempered with a degree of risk which is measured in terms of materiality and seriousness, in relation to a particular patient.