It has been settled law since the case of R v Brown(A)  1 A.C. 212, HL that while consent may be a defence to injury short of a wound or amounting to common assault an individual cannot consent to intentional injury which is more than transient that amounts to actual bodily harm or worse. This is so even between consenting adults in the privacy of their bedrooms, dungeons or otherwise.
Our jurisprudence is well ahead of EL James and Hollywood. The case of Brown concerned a group of men who willingly and enthusiastically participated in acts of violence for the sexual pleasure of giving and receiving pain (commonly referred to as bondage domination sadomasochism or BDSM). The sexual orientation of the participants has no bearing on the legal principle established.
On appeal against convictions for actual bodily harm and malicious wounding the Court held “The satisfaction of sadomasochistic desires does not constitute good reason for the infliction of bodily harm or a wound”
In the further case of Laksey, Jaggard and Brown v UK., 24 E.H.R.R. 39, the European Court of Human Rights confirmed the principle in finding that there was no violation of the Article 8 Right to respect for one's private and family life, home and correspondence as a result of their conviction.
The CPS website rehearses the level and types of injury capable of amounting to actual bodily harm and malicious wounding.
While unsurprisingly silent on BDSM the guidance points to injury inflicted through strangulation as an aggravating factor in decisions on whether and if so what offence to charge.
The Definitive sentencing guideline in respect of Assault similarly offers cold comfort. The circumstances surrounding an injury sustained as a result of BDSM echoes several of the aggravating and other factors indicating higher culpability thereby making the imposition of a custodial sentence a real risk on conviction.
Those still inspired by 50 Shades of Grey should proceed with their eyes open and with caution.