I think the charge would be Indecent Assault under S70 AFA. IIRC from previous CMs I've been involved with (as a member!), the ingredients of the charge are "an assault" ie that actual contact took place and that it should be "indecent" ie to have a element which the average person would consider to be indecent.
Of course, consent would be an absolute defence -which it can't be in some cases - eg setting fire to people at Happy Hour.......