To determine the criminal liability of Lancelot, it is necessary to establish if Lancelot will be guilty for homicide, whether it is murder or manslaughter. In addition to this, it is also crucial to establish what defences Lancelot might have against the charges and their weight from the fact pattern of the case. After these issues are evaluated, the criminal liability for Lancelot will be established. According to common law, the law for homicide is the unlawful killing of a human being in the Queen’s peace.
Murder is an unlawful killing with ‘malice aforethought’ whereas manslaughter is an unlawful killing without ‘malice aforethought’.  It is fairly straightforward that Lancelot has committed the actus reus of an unlawful killing as Guinevere died from Lancelot’s act which was his attempts to muffle her protests. Firstly factual causation is established as the ‘but for’ test has to be applied(R v White).  Guinevere would not have died but for Lancelot’s actions so Lancelot factually caused her death.
Legal causation is also established as Lancelot’s actions were directly substantial to Guinevere’s death and there was no novus actus interveniens; an intervening act that breaks the chain of causation. Furthermore, the thin skull principle can also be applied here where “the defendant has to take his victim as he finds him”.  Even if Guinevere was physically vulnerable to such acts, Lancelot would be held liable for her death despite his awareness of it due to this principle(R v Hayward).  It is now important, to establish if Lancelot had the required mens rea for his actions to be classified as murder or manslaughter.
Mens rea for murder is established when the defendant has an intention to kill or cause grievous bodily harm to the victim(R v Vickers).  Following the fact pattern of the case, Lancelot acted in such a way to muffle the protests of Guinevere while he attempted to engage in sexual intercourse with her not because he had an intention to kill or cause grievous bodily harm. Furthermore, a subjective test has to be applied to determine if Lancelot had oblique intention; which entails that he must have foreseen that Guinevere’s death was virtually certain as a consequence of his actions(R v Woolin).
 Lancelot would not have foreseen that Guinevere would die or suffer from grievous bodily harm from his act of muffling her unless it was significantly dangerous. Therefore, Lancelot would most likely be convicted of involuntary manslaughter as he did not have the required mens rea to be convicted of murder. However, if Lancelot is still charged with murder, his appropriate defence would be intoxication as other partial defences of diminished responsibility, loss of control and suicide pact do not apply to the facts of the case.
It can be argued that his voluntary intoxication is able to negate the mens rea of murder even though it was a specific intent crime(DPP v Beard). Therefore, his partial defence of intoxication could reduce his conviction from murder to manslaughter(R v Sheehan and Moore).  To conclude, Lancelot will most probably be liable for involuntary manslaughter in which he does not have any substantial defences except intoxication. This is due to his lack of mens rea which will reduce his conviction from murder to manslaughter.
The courts will also evaluate his level of intoxication and the actual medical cause of Guinevere’s death, and sentence him accordingly. Arthur kills Guinevere with his sword In order to determine the criminal liability of Arthur in this situation, it is necessary to establish if Arthur will be guilty for murder or not from his actus reus and mens rea. His grounds for defence will also be considered to evaluate his criminal liability. Murder can be defined as the unlawful killing of a human being under the Queen’s peace with malice aforethought and an intention to kill or cause grievous bodily harm.
It is fairly clear that Arthur has committed the actus reus for murder by killing Guinevere with his sword. Firstly, the factual causation is fairly obvious from the application(R v White), as Guinevere would not have died but for Arthur using his sword to kill her which shows the Arthur caused Guinevere’s death. Furthermore, the test for legal causation can also be applied as Arthur’s act was the significant cause of Guinevere’s death and there was no novus actus interveniens or a break of causation.
Following the fact pattern of the case, Arthur seems to have the required mens rea for murder as he has the intention to kill or cause grievous bodily harm upon the victim. The element of direct intent is notable in Arthur’s act and it is without a doubt that direct intent will be established without consideration of oblique intent(R v Janjua & Choudhury).  Even if Arthur may not have intended to kill Guinevere, it will be found that he intended to cause at least grievous bodily harm(R v Cunningham). 
However, Arthur is most likely to put forward his partial defence of “loss of control” under 54(1) of the Coroners and Justice Act 2009 that can reduce his conviction of murder to manslaughter; Firstly, it has to be established if Arthur killed Guinevere due to a loss of self-control. It is most likely that that this was not an act of revenge which qualifies as loss of control(R v Ibrams & Gregory). Arthur can substantiate his defence by “a justifiable sense of being seriously wronged” under s. 55 (4) as he said "If there is one thing I cannot tolerate it is sexual infidelity! " when he saw Guinevere and Lancelot.
However, it is uncertain if there were other factors that could could have led to his loss of control that may constitute to “circumstances of extremely grave character” under S. 54(4)(a) of the act.  On the other hand, a basis for sexual infidelity is to be disregarded under s. 55(6)(a).  Unless there are other circumstances that sexual infidelity may contribute to, it will not amount to loss of control(R v Clinton).  Therefore, Arthur’s partial defence of loss of control due to sexual infidelity is most likely to be unsuccessful as the courts have imposed strict limits to the doctrine unlike provocation.
 It will also be very problematic for the courts to establish an objective test by the use of the reasonable man upon Arthur’s actions and could cause a lot of controversy(DPP v Camplin).  To conclude, Arthur will be liable for murder for the death of Guinvere as he constitutes the required actus reus, mens rea and lack of substantial defence. However, his sentence will depend on other mitigating circumstances which are uncertain in the fact pattern that could alter his conviction such as his relationship with Guinevere and Arthur’s subjective capability. Lancelot seriously wounds Arthur
Lancelot will most likely be liable of wounding and inflicting grievous bodily harm under s. 20 of the Offences Against the Person Act 1861, "whosoever shall unlawfully and maliciously wound or inflict any grievous bodily harm on any other person, either with or without a weapon or instrument, shall be guilty of a misdeamenour… " Lancelot has committed the actus reus of unlawfully inflicting grievous bodily harm to Arthur as he has been “seriously wounded”. This suggests that there is a break in the continuity of the skin(Moriarty v Brookes) and that grievous bodily harm has been inflicted.
It is now important to establish if Lancelot had the mens rea or intention to cause grievous bodily harm to Arthur. According to the fact pattern, it suggests that Lancelot was acting in self-defence when Lancelot started attacking him and Guinevere even though he should have foreseen and appreciated that he would cause serious harm(R v Parmenter).  As he was acting in self-defence, it could be found that his actions may be lawful under s 3 of the Criminal Law Act 1967.  Furthermore, the prosecution will raise questions of necessity and reasonableness of Arthur’s actions following (R v Williams).
After they are satisfied, the jury will apply the objective test of the reasonable man to test the reasonableness and excessiveness of Arthur’s act.  To conclude, Lancelot will most likely be liable for inflicting grievous bodily harm under s 20 of the Offences Against the Person Act 1861 unless his grounds of self-defence are substantial enough for him to be acquitted. However, this will depend on the courts and their interpretation of his level of intoxication, subjective capabilities and his reasonableness of seriously wounding Arthur.