I don't think that it is a criminal offence to print and sell this tshirt,tbh.
Which doesn't mean that we should not protest against it.
Last week there was a program on German TV about Rohypnol. They interviewed young girls who had been raped on holiday. And a guy who made and sold Rohypnol. It was shocking how easily it could be bought and how toothless the German police are in this area. And how few women knew about it and how to prevent this happening to them.
No idea if the situation is similar in UK, but I was really surprised to learn how little the police could do to stop the sale of this.