Hard core porn - or R18 - is still sale restricted, although now legal in the UK. Mark & Gary are very right in consulting their lawyer about this. By having them listed at the moment, it is a general category. BUT by segregating them to their own section may have HUGE implications. Plus M & G would HAVE to advise sellers on the correct way to list, describe, AND get said items to the buyer.
Don't blame G & M, blame our ****ty Victorian laws in this country.