United Kingdom law on ballbusting and CBT seems to be intentionally vague, while in most cases S&M is legal, technically some acts fall in to a grey area. In certain cases it may be illegal to possess photographs or videos of acts and in some cases illegal to take part in them.
For example, in the UK it is illegal to possess images that depict any act in which the skin of the genitals is pierced or where blood is drawn, I think you would agree that this extreme subset of CBT is a rare and different fetish.
The law is there to protect the general population and with ballbusting there are some risks, in the same way most sports contain a certain amount of risk. We all hope not to end up in accident and emergency following a game of rugby or badminton but it does occasionally happen.
Sex toys designed for CBT are legally sold in the UK but any image that depicts an item being inserted into the penis which is not designed for that purpose could put you in hot water.
While the law seems to be a little grey in some areas, it is very clear in others. Any sexual act must take place between two consenting adults of legal age. If a BDSM scene depicts a person who is restrained or gagged, it maybe unclear as to whether that person is consenting or not.
Even when consent is given, S&M must be practices safely and shouldn't cause any serious harm to the participants, anything that leaves more than a "transient and trifling" mark is legally regarded as assault or grievous bodily harm in English law. Consent isn't a defence to criminal liability for any injuries caused.
Of course, it would be up to a court to decide what passes as transient but according to the British Board Of Film Classification (BBFC) a DVD rated R18 can include the reddening of the skin, but purpling or breaking of the skin crosses a line.
The golden rule for any BDSM act is SSC. Keep it Safe, Sane and Consensual. A common principles that guides relationships and activities in the BDSM community.
A BDSM acts should be carried out once all possible steps have been taken to identify and prevent any potential health risks. Activities should only be undertaken in a sane and sensible frame of mind and most importantly, all activities should involve the full consent of all parties involved.
