Advice needed please

My boyfriend was drugged and raped about 6 months ago now.It's still very raw in our minds,probably more mine than his.He's had a pretty tough life so far and not too good at opening up.Whereas I am very emotional person I still cry thinking about it now.He didn't go to police as he felt ashamed and embarassed.
Last night he told me that one of his abusers came into his work (same place he was drugged)about 4 weeks ago.They had a photo (don't want to know what of but i can imagine) and asked him for money otherwise they would show everyone at his work.He saw photo so knows they are not bluffing! He gave them £20.Now he is being blackmailed for more money to stop them distributing these photos (they have more than 1).I told him to go to police and tell them EVERYTHING and he said he would but will he be taken seriously? Can anything be done about rape and blackmail? It's going to be his word against theirs isn't it? I feel sick not only thinking about what they did to him but about who else they have probably done same thing to