Consent is a limited defence in that it can only be used for minor non-fatal offences (usually up to s.47, Assault Occasioning Actual Bodily Harm).
If a defendant can successfully raise a defence of consent then this will result in a complete acquittal.
However as it results in such a serious outcome, it is very difficult to satisfy a defence of consent.
Some would even argue that whilst we are looking at the consent of a victim, in that respect it isn't even really a defence.
R v Donovan ,
R v Donovan 
D had invited the Victim (a 17 year old girl) back to his garage, where he canned her 8 times for his own sexual gratification.
D was charged with Indecent and Common Assault. Whilst he was originally convicted, his conviction was quashed by the Court of Appeal.
The COA was cautious in the acquittal though.
Whilst there was overwhelming evidence to show that V had consented at least in some degree to the harm, this would not be applied universally.
As Lord Hewart CJ asserted:
"An unlawful act cannot be rendered lawful because the person to whose detriment it is done consents to it. No person can licence another to commit a crime".
Essentially the defence is limited on a case by case basis.
areas to be considered with consent
1. Real Consent
2. Implied Consent
3. Consent to Minor Harm/ Consent in Sporting Events
4. Mistaken belief in Consent
5. Medical Procedures and Consent
Just because someone agrees to a level of harm does not mean that this consent has been obtained willingly, or that they are aware fully of what they are consenting to.
The law is quite clear on the issue of real (true) consent, if consent has not been obtained freely (i.e. a defendant has used force) or has been obtained through deception, then this is not consent at all.
R v Tanassum 2000,
R v Olugboja 1982,
R v Dica 2004,
R v Tanassum 2000
D had approached a number of women as part of his employment as a programmer of medical software.
He asked a these women if he could perform a breast examination to check for breast cancer.
All the women consented as he carried with him a range of medical equipment which implied he had medical experience or qualifications, he had neither.
Whilst D's reason was not for sexual gratification (he was developing a programme to help test for breast cancer) it was misleading.
D was charged with Indecent Assault (now Sexual Assault) and argued that this could not be an assault as all the women had consented freely to his behaviour. The Court of Appeal approved earlier comments at the original trial by Livesey Q.C. who said that:
"Consent in such cases does not exist at all, because the act consented to is not the act done. Consent to surgical operation or examination is not consent to sexual connection or indecent behaviour".
R v Olugboja 1982
D and his friend had met V1 and V2 at a club and taken them back to their student accommodation.
D's friend had already raped V1 and V2 in the car whilst D prepared the bungalow. V1 told D what had happened and asked him to leave her alone. D asked to remove her trousers, which she did. D then told V1 that he was going to **** her.
D had intercourse with V1, during which she did not scream, protest or cry. She only struggled when she thought that D would ejaculate inside her.
At D's trial for rape he argued that her submission amounted to consent.
The COA disagreed and held that her submission was not consent, it was neither free nor fair and she was only consenting because of the fear of force upon her. The issue of whether V consents should always be left to the Jury.
R v Dica 2004
D had contracted HIV a number of years earlier and on two separate occasions had had unprotected sex with V1 and V2, whilst knowing that he was HIV positive (they were both unaware of this and crucial maintained in court that they would not have initiated sexual intercourse if they had known).
D was commented to have said "God forgive me" during each bout of intercourse.
D was found guilty of inflicting biological G.B.H. (s.20).
In this situation the victim's consent was invalid;
D was sentenced to 4 ½ years' imprisonment.
If you think back to Collins v Wilcocks in which the court outlined that any touching can in theory be a battery, however we must be prepared for the exigencies of everyday life (i.e. the normal pushing, shoving, back slapping and horseplay that come from living in a busy society).
This is often referred to as Implied Consent,
Wilson v Pringle ,
Wilson v Pringle 
D and V where both at school together.
D had jumped on V's back and V had fallen over suffering minor injuries.
At D's trial it was argued that this kind of 'horseplay' between two people in a crowded place was all part of the ordinary jostling of everyday life.
In such situations we are implicitly consenting to a range of levels of interaction, some of which may constitute battery.
In these situations it is unlikely that we can claim any sort of injury in criminal law.
Consent to Minor Harm/ Consent in Sporting Events
The first issue of note is that we cannot consent generally to any harm above a battery.
Therefore a s.47, s.20 or s.18 offence cannot in theory be consented to,
Attorney-General's Reference No.6 of 1981,
R v Brown (1993),
R v Wilson 1996,
R v Barnes 2005
Attorney-General's Reference No.6 of 1981
D 18 and V 17 had a disagreement in a street,
they agree to have a fight and D is arrested as V comes off the worse,
D is charged with assault occasioning ABH,
the court found that despite the consent of both parties it was still an offence,
Lord Lane set out in this case that ABH will always be unlawful regardless of consent,
he also stated that if done within the rules and guidelines required it will be covered by consent such as in;
1. games and sports
2. lawful chastisement and correction
3. medical procedures
4. dangerous exibitions
R v Brown 1993
D was one of a number of homosexual males who engaged in acts of sadomasochism,
such things as putting fish hooks through each others foreskin and hammering a nail through the testicle,
it all took place in private dwellings and was filmed,
D and others were charged with s.47 assault occasioning ABH with appeals dismissed,
the HoL held that such behaviour was entirely criminal and all consent was invalid,
this was because;
1. the harm in some cases was more than trifling or transitory so the consent is invalid,
2. such behaviour was not in the 'public interest and was described as a 'cult of violence'
R v Wilson 1996
V asks D to brand his initials on her buttocks,
he brands it onto her with a hot knife,
V goes to the doctor with an unrelated incident and the doctor reports it to the police,
D is charged with s.46 ABH but found not guilty on appeal,
the victim had not only consented but had it instigated against her,
the CoA drew a deliberate distinction with the Brown verdict as it was similar to a tattoo which could be consented to in everyday life,
R v Barnes 2005
D was playing in an amateur football match and went into a sliding tackle with V who suffered serious leg injuries as a result. D was charged with unlawfully and maliciously inflicting G.B.H.
under s.20 of the Offences against the Person Act 1861. D appealed on the grounds that this had taken place with a legitimate sporting environment.
The Court of Appeal set out the following guidelines on consent:
(1) Consent isn't normally available for A.B.H unless it is one of the public policy exceptions set out in A-G's Ref .
(2) In contact sport, any harm which goes beyond what a player could reasonably have expected as part of the sport is NOT covered by consent.
(3) In bodily contact sports (such as Rugby) the actual contact is always covered by consent, even though accidents and injuries may occur from this.
To decide whether the conduct is criminal or not, the COA suggested the following considerations:
(a) Intentionally inflicting harm will always be a crime
(b) Recklessly inflicting harm- Either during the game or 'off the ball'
(c) Off the ball- A moment of madness outside the rules of the game is likely to be criminal
(d) During the game- if it was within the rules then likely not to be criminal.
Mistaken belief in Consent
In some situations we may encounter a defendant who actually believes that a victim has consented, even when they actually haven't.
In these situations as long as the belief of the defendant is genuine and can be proven, then this will still amount to a defence of consent.
R v Jones 1986,
R v Fotheringham 1989
R v Jones 1986
V1 and V2 were approached by group of boys in the school yard.
They were picked up by D and his group who then proceeded to throw both V1 and V2 into the air and then allowed them to fall.
One suffered a broken arm, whilst the other suffered ruptured spleen. D was charged with s.20 G.B.H.
On appeal D's conviction for G.B.H. was overturned.
The trial Judge had not allowed the Jury to consider a defence of mistaken consent.
The COA held that rough and undisciplined horseplay could be considered under a mistaken consent, as it would appear that D genuinely believed that V1 and V2 had consented to this.
This was even though the belief was clearly unreasonable.
R v Fotheringham 1989
D and his wife had been out for an evening meal and had hired V (aged 14) to babysit for them.
W had told V that once the children were asleep she could sleep in their bedroom if she so wished, D was not informed of this.
When D and W returned home, D went upstairs and got into bed with V.
He began sexual intercourse with her and stopped when his wife walked in and realised that he was in fact raping the babysitter.
D was charged with rape and argued that he would not have had sexual intercourse with V, as he honestly and truly believed he was having sex with his wife.
D was found guilty and his appeal was dismissed. His mistake was based on self-induced intoxication.
Medical Procedures and Consent
A mentally capable adult has the final say over any treatment they receive. Conversely a child (someone under the age of 18), someone with a mental health condition or someone who cannot consent for any other reason (such as being in a coma) then medical professions must reasonably attempt to contact relatives.
If this isn't possible than life saving treatment will be performed even without true consent.
Re: J (Circumcision) 2000,
R v Richardson 1998,
R v Flattery 1877
Re: J (Circumcision) 2000
J had been born into a family in which the father was a Muslim but were the mother was a non-Muslim.
At the age of 5 J's parents had separated and lived with his mother in a secular household.
D had requested that his son be circumcised in accordance with Islamic hadith traditions, however J's mother strongly disproved of this.
After much debate the issue was taken to court.
The court considered a range of factors in deciding upon whether to allow J's circumcision.
The most important issue was whether there was any intention to bring J up as a practising Muslim.
It was found that D was not actively practicing his religion and there was no desire for this on the part of the mother.
The court held that no medical treatment could take place without its consent.
R v Richardson 1998
D had been suspended from practicing as a Dentist since 1996 by the General Dental Council.
However she continued to treat patients for some time after her licence was suspended.
She was charged with 6 counts of assault but tried to raise a defence of consent, as all her patients had consented to the medical procedure and she had not harmed any beyond the levels normally associated with dental treatment, however none had been told of her suspension.
D was found not guilty. The principle here for medical treatment is the same as that for sexual assault cases.
A potential victim had not been deceived as to the nature of the act (it was routine treatment) they had only been deceived as to the qualification of the act.