It can be argued that consent is not a defence as consent means there has been no unlawful act. In deciding whether consent is to be allowed the relevant considerations are in what circumstances a person is able to give consent and whether genuine consent is given. This area of the law has attracted some criticism and calls for reform.
There is a lack of clarity over the reasons behind allowing or denying consent.
Level of harm
Defendant inflicted a serious leg injury upon the victim. Defendant had attempted to make a sliding tackle during an amateur football match. Defendant accepted that the tackle had been hard, but maintained that it had been fair and that the injury caused had been purely accidental. Defendant was convicted of a S20 offence under the Offences Against The Person Act (OAPA) 1861.
Court of Appeal quashed the defendant’s conviction. Court also ruled that criminal prosecutions should be reserved for situations which were
.. sufficiently grave to be properly categorised as criminal....
So it could be based on the level of harm, with serious harm cases being denied.
Defendants nailed the victim to a wooden cross, piercing his hands with six inch nails. Victim had organised to be crucified on Hampstead Heath and defendants were acting at his request.
Defendants found guilty under S18 (OAPA 1861). and were not allowed to rely on the victim’s consent.
However, if this is the case it seems inconsistent that consent is allowed in situations where injuries are common, for example boxing or horseplay.
Defendants, newly qualified RAF officers, had a party to celebrate qualifying and took part in drunken horseplay. Defendants set fire to the victims fire resistant clothing and the victim suffered serious burns.
At a court martial, the defendants were convicted of S20 offence under OAPA 1861. On appeal the convictions were quashed and consent argument was allowed. Intoxication was irrelevant as S20 not a specific intent crime.
Watson v BBBC 
Victim was injured in a boxing match supervised by the defendant, British Boxing Board of Control (BBBC). The defendant was expected to provide medical care to the victim, a boxer, during a fight. Victim sustained serious injuries which left him in coma for 40 days and 6 years in a wheelchair.
Victim sued the defendant in negligence, and was awarded damages of over £1 million. Decision was upheld by the Court of Appeal, who noted that a doctor must be ringside.
Decision highlights the fact that boxing is considered inherently dangerous and did not allow consent in this instance.
Consent may be present but this may not be sufficient if the aim of the activity is to cause harm.
Defendants participated in sadomasochistic homosexual activity and no one suffered permanent injury. Defendants argued the acts were consensual. The judge did not allow the argument so the defendant’s plead guilty to assault occasioning actual bodily harm and unlawful wounding.
On appeal the court had to decide whether consent should have been allowed to be raised. The court confirmed consent could be only be used in cases of battery because causing any greater injury was not in the public interest.
Defendants convicted of offences under OAPA 1861.
..violent cruelty is injurious and predictably dangerous. I am not prepared to invent a defence of consent for sadomasochistic encounters….
The need to protect the vulnerable has also been raised as an issue with consent.
Burrell v Harmer (1967)
Defendant tattooed the victims, 12 and 13 year old boys and caused actual bodily harm. Victims consented to being tattooed but the court would not allow the defence of consent.
It was held that where a victim was unable to appreciate the nature of the act consent could not be truly given.
However, protection of young victims is not always maintained in UK law.
A v UK (1998)
Defendant often severely beat the 8 year old victim with a garden cane. Defendant argued that such action was reasonable and necessary because the victim was a difficult child.
European Court of Human Rights found defendant’s action to be a breach of Article 3 of the Convention for the Protection of Human Rights and Fundamental Freedoms 1950, which protects against inhuman or degrading punishment.
It was held that the UK had failed to provide adequate protection to children in such situations.
The application of the law in relation to whether consent is valid seems to be unclear, in terms of the victim’s necessary knowledge.
In cases of fraudulently obtaining consent conflicting conclusions have been reached.
Defendant, a suspended dentist had carried out treatment on patients. Patients consented but would not have done so if they knew the defendant was disqualified.
Consent was accepted in this case and defendant not found guilty of assault.
Defendant, who knew he was HIV positive, had unprotected sex with the victims, who became infected. Victims claimed they did not know about his HIV and if they had done would not have engaged in unprotected sex. Defendant was convicted of S20 offences under OAPA 1861.
Court of Appeal found the victim needed to consent to the risk of catching the disease. Court also quashed conviction and ordered a retrial on the grounds of a misdirection.
In some cases of mistaken consent, the argument has been allowed.
Richardson and Irwin (1999)
Defendants and victim were students who often indulged in horseplay. Defendants had drunk around five pints when they dropped the victim from a balcony, believing he consented. Victim suffered serious injuries. Defendants convicted of S20 offences under the OAPA 1861.
Court of Appeal allowed the appeals and held their belief in the victim’s consent should have been considered.
This is in contrast to decisions in cases such as Leach  or Brown (1993) where genuine consent existed but was not allowed.
There is some inconsistency in whether individual freedom to engage in consensual activity is should be allowed.
Attorney General’s References (No6 of 1980) 1981
..It is an essential element of an assault that the act is done contrary to the will and without the consent of the victim.. it’s not in the public’s interest that people should try to cause, or should cause, each other bodily harm no reason....
In some cases, consent is accepted, despite serious harm. Such cases raise the issue of whether consent should be reflected in sentencing but not in the verdict.
Defendant branded, with a hot knife, his initials on his wife’s buttocks. The victim had requested the homemade tattoo. She had to seek medical attention for burns. Defendant was convicted of an offence under S47 under the OAPA 1861.
Court of Appeal found the branding was not an unlawful act despite the injury caused. It was found to be a situation of
personal adornment and not in the public interest to criminalise such consensual acts.
Whereas, in other cases the courts will intervene despite the presence of consent.
Lord Mustill dissenting:
.. The state should interfere with the rights of the individual no more than is necessary... .
Consent is not allowed to be given for killing and raises complex arguments in relation to euthanasia.
If a patient is capable of giving consent then a doctor has no authority to treat them without their consent. However, a patient is not allowed to ethically refuse treatment in order to bring about their own death. There is no legal right to suicide or for others to be involved in helping someone to die.
Concerns exist that in allowing some competent patients to decide to die would leave an avenue for the vulnerable to be ‘killed off’. Legislation to allow euthanasia would allow private citizens, doctors, to kill others and has caused serious arguments.
Dianne Pretty was paralysed by motor neurone disease. Her condition worsened which made it impossible for her to move or communicate easily even though her mental faculties remained. She wanted to be able to choose the time of her own death and would need her husband’s help. She took a case to try and ensure if he assisted in her suicide he would not be prosecuted. She argued that Article 2 of the European Convention on Human Rights protects the right to life and right to choose manner of death.
The House of Lords and European Court of Human Rights, both found that Article 2 did not provide the right to die. The courts found the protection of vulnerable citizens was of paramount importance. Diane Pretty’s case failed.
R (on application of Purdy) v DPP (2009)
Mrs Purdy, suffered from multiple sclerosis and declared her wish to travel to a country where assisted suicide was lawful to end her life when her illness became utterly unbearable. She sought information in order to make an informed decision about whether to ask her husband to help her travel.
Under S2 of Prosecution of Offences Act 1985, the DPP is obliged to give guidance to prosecutors on general principles to be used in deciding whether to prosecute in cases involving aiding suicide. The guidance gave little indication about issues relevant to those assisting people to travel abroad to commit suicide. Mrs Purdy asked for clarification this point and the DPP refused to issue further guidance.
House Lords heard Mrs Purdy’s judicial review request. The House of Lords held that the DP should issue guidelines.
Assisted suicide remains unlawful under the Suicide Act 1961. The new DPP guidelines still leave the situation unclear and mean those who assist someone to travel abroad to commit suicide may be liable for prosecution.
Some cases have moved closer to allowing the withdrawal of life sustaining treatment.
Airdale NHS Trust v Bland 
Mr Bland was severely injured at the Hillsborough disaster and was unconscious and in a vegetative state. He continued to breathe by himself and his digestive system still functioned. However, he could not communicate, was incapable of voluntary movement and had no sensory abilities. Doctors agreed there was no hope for recovery or improvement in his condition. After three years doctors and his family applied to the court for a decision on whether it was lawful to stop his artificial hydration and nutrition, which would lead to his death.
House of Lords decided that his treatment could be stopped. They made a number of findings in coming to this conclusion. Namely, artificial nutrition and hydration is a form of medical treatment and there is no distinction between withholding treatment (an omission) and discontinuing treatment.
Also, in order to make such a decision, it should be considered whether it is in the best interests of the patient that his life should be prolonged. This assessment should include the previous stated wishes of the patient and views of close relatives.
.. the law draws a crucial distinction between cases in which a doctor decides not to provide, or to continue to provide, for his patient treatment or care which could or might prolong his life, and those in which he decides, for example by administering a lethal drug, actively to bring his patient's life to an end.. the former may be lawful, either because the doctor is giving effect to his patient's wishes . . . or even in certain circumstances in which.. the patient is incapacitated from stating whether or not he gives his consent. But it is not lawful for a doctor to administer a drug to his patient to bring about his death, even though that course is prompted by a humanitarian desire to end his suffering, however great that suffering may be.. So to act is to cross the Rubicon which runs between on the one hand the care of the living patient and on the other hand euthanasia....
However, this remains a very controversial area of law. It is a subject with such wide ranging issues that infringes on morals and ethics in a way which can only dealt with through legislation. Most would agree for judges to change the position through case law would be very wrong and an inappropriate use of power
Proposals for reform
Proposals for reform on certain aspects, such as in relation to euthanasia have been made by a wide range of campaigning organisations. More formal proposals are less common.
The Law Commission has expressed several views on the rules surrounding consent in relation to investigations into different aspects of the law.
Consent in sexual offences, written in response to Government consultation, made the key recommendation was that
.. subsisting, free and genuine agreement should count as consent to a sexual act by another.... The Government then implemented the Sexual Offences Act 2003. However, problems still exist in some cases.
Law Commission’s 1994 consultation paper
Consent and Offences Against the Persondiscusses the view that a a person's body is their own, and that the law has no place in dictating what can be done with it. However, the approach is rejected with the Commission highlighting illegal drugs as an example where the law limits complete bodily freedom.
Level of injury
Law Commission’s 1994 consultation paper
Consent and Offences Against the Personagrees the law should set a limit to the injury to which a person may consent but that certain special categories should be exempt from the law and proposes ritual circumcision, ear-piercing, tattooing and dangerous exhibitions should be included.