A significant proportion of the UK engage in consensual sexual activities which cause some bruising or cuts. This could be spanking, flogging etc. These injuries are not serious and do not require medical attention. Yet the participants risk imprisonment.
As a consequence of the Brown ruling even causing a love bite is an illegal activity.
The injuries are slight compared to those suffered by those engaging in contact sports such as football, rugby, martial arts and boxing. Yet sports players are not prosecuted.
In a typically puritanical British way sports is seen as a "good reason" for such injuries but sexual pleasure is not.
The effect of the Spanner case is to inhibit education in the field of BDSM. Without education and open discussion people are more at risk of engaging in unsafe activities.
For more information see www.spannertrust.org