Theoretically consent is available to murder
Theoretically consent is available to murder and all non-fatal offences against the person. However in actuality, consent could not be used for anything more than assault and battery. Essential questions of morality and ethics are raised by the degree to which the state be supposed to employ criminal sanctions to restrict a sane adult in his/her consent to the infliction of harm on his/her person. On the basis of public policy, English Law confines the legitimacy of consent by reference to the level of harm and the circumstances in which it is inflicted.  It is in respect of the deliberate infliction of physical harm that the law has encountered difficulties in determining where the line should be drawn to mark the limits of personal autonomy. The matter is complicated further by questions as to what constitutes informed consent, and whether the law does and should distinguish between consent to inevitable physical harm and consent to the risk of harm.  The law strives to achieve a balance between personal autonomy; i.e. the right of individuals to control what happens to them, and prevention of harm (to individuals and to society).  Factual consent to actual bodily harm or more serious levels of harm; i.e. wounding, serious harm, death, is not lawfully accepted unless the activity concerned is one which the courts or Parliament have recognised to be in the public interest.  The Law Commission propose raising the level of harm to which a person is entitled to consent in general circumstances to harm falling below a new concept of ‘serious disabling injury’.
The Court of Appeal stated in the case of Attorney-General’s Reference (No. 6 of 1980)  , that ‘It is not in the public interest that people should try to cause or should cause each other actual bodily harm for no good reason. Minor struggles are another matter. So...it is immaterial whether the act occurs in private or in public; it is an assault if actual bodily harm is intended and/or caused. This means that most fights will be unlawful regardless of consent.’ The question raised is not just whether the victim consented but also whether there was nothing contrary to the public interest in what the defendant did. The expression ‘no good reason’ can be said to be vague and unhelpful. Reasonable people may differ in their opinion as to whether one type of behaviour, for example tattooing, can be seen as good or not. In the case of R v Brown  , It can be assumed that the majority apparently started from the proposition that all harm was criminal unless there was a good reason, whereas the minority preceded from the basis that harm to which the victim consented was lawful unless there was a good reason from punishing the accused. 
Even though the language utilized in the cases mentioned above cases mirrors this restrictive approach, the general pattern of immunity reflects a more libertarian emphasis. Harmful activities as difficult to justify as tattooing, circumcision, boxing and dangerous horseplay are all considered lawful, while it would be an unusual claim to persist that such activities were needed ‘in the public interest’. It is probably more accurate to say that positive public policy reasons in favour of the activity are necessary only in the case of intentional harms. 
The law does not prohibit all force on the person, but only the unlawful use of force. For example parents may punish their children moderately. The law is bases on reasonableness, yet it may well not reflect public opinion. In the Case of R v Donovan  , Swift J stated that with some exceptions: ‘It is an unlawful act to beat another person with such a degree of force that the infliction of bodily harm is a probable consequence and when such an act is proved, consent is immaterial.’ In this case the defendants canning of the victim with her consent for their mutual sexual enjoyment rendered him liable under section 47 of the Offences Against the Person Act 1861. 
The basic rule stated by Lord Lane CJ in Attorney-General’s Reference (No. 6 of 1980)  , where the victim suffered actual bodily harm in the form of a bloody nose: the accused is guilty of a crime even though the victim has consented ‘if actual bodily harm is intended and/or caused’. This principle was approved by the House of Lords in the Landmark case of R v Brown  . It should be noted that Lord Lane CJ’s proposition covered a situation where the accused does not intend and is not reckless as to occasioning actual bodily harm. It is sufficient that such harm occurs. The use of ‘and/or’ is a strange one. It correct, it means that an accused will not be able to rely on the victim’s consent if he intends actual bodily harm but such injury does not happen. Therefore, it can be stated that in principle, consent is a defence to assault and battery, as indeed the House of Lords held in R v Brown  and, therefore, if no actual bodily harm is occasioned, the accused should not be guilty of assault occasioning actual bodily harm. Intending an offence is not the same as committing an offence. 
If the accused lacked the mens rea for the offence, he is not guilty even though the victim has consented in fact to behaviour she could not in law consent to. This can be seen through the case of R v Slingsby  , where the accused was not guilty of constructive manslaughter because he gave no thought to any risk of injury when he penetrated the victim’s anus and vagina with his and his ring cut her. He had no mens rea for the offence of wounding on which the charge was based. Therefore, he was not guilty of manslaughter. In this case the issue of consent was irrelevant.  Therefore, a fair assumption would be that if there was not mens rea present then consent would be irrelevant as a defence.
In the case of Attorney-General’s Reference (No. 6 of 1980)  , Lord Lane CJ proposed that the exceptional categories where bodily harm could be consented to were all categories where the activity concerned was of social benefit and consequently advantageous to the public interest. 
Harmful activities as difficult to justify as tattooing, circumcision, boxing and dangerous horseplay are all deemed lawful although it would be an unusual claim to insist that such activities were needed ‘in the public interest’. It is probably more accurate to say that positive public policy reasons in favour or the activity are necessary only in the case of intentional harms.
The law commission proposed that if a seriously disabling injury resulted, consent should be invalid on the ground that the victim had not truly consented to it because such harm is contrary to his interests. A major criticism of this proposal is that the level of harm to which the ‘victim’ can consent is high. A seriously disabling injury is not minor harm. No account is to be taken of whether the injury was remediable by surgery or not. Consent to lesser injuries would be allowed provided that it was valid and was consent to the type of injury caused. 
The Mode Penal Code view is that consent of the victim negates the crime if the consent “precludes the infliction of the harm or evil sought to be prevented by the law defining the offense."(M.P.C & 2.11(1)). More particularly, the Code provides that where a crime involves threatened or actual bodily harm, consent is a defence it the bodily harm is not serious or part of a lawful athletic contest or competitive sport. 
In Brown, sadomasochists who had engaged in consensual beatings and genital torture which had not resulted in any participant receiving medical attention were convicted of offences of assault occasioning actual bodily harm. The House of Lords, by a majority of 3 to 2 upheld the convictions. By doing so the House of Lords recognised certain categories of activity in which the law would recognise effective factual consent to injury as valid in law.  These include surgery, sports, horseplay, body modification, religious flagellation and the risk of sexually transmitted diseases.
The case of Brown was considered by the European Court of Human Rights in Laskey v United Kingdom,  with the Court unanimously holding that the prosecution, conviction and sentence did not contravene Article 8 of the Convention. The Court doubted whether the activities even fell within the protection of Article 8. On the assumption that they did, the Court concluded that the prosecution was necessary and proportionate to the legitimate aim of the protection of health and possibly also the protection of morals. The Court recognised that the margin of appreciation provided national courts the scope to prescribe the level of physical harm to which the law should permit an adult to consent.