Hi Daniel,
Remember this is my opinion and only my opinion. I am NOT a doctor.
You need to go to a GI doc. I'd start with a family doc because here in the states you have to be referred. I don't know how it works in the UK. You need some more tests! Even if it's IBS you need to have futher tests to rule out problems that IBS mimics. Some of of the things IBS mimics could be quite dangerous. (I'm not trying to scare you honey, it's just the facts.)
I can't tell you if it's IBS but I don't remember ever hearing that black stools were a part of IBS. The rest could be but if it were me I wouldn't take a chance.
Just a note: You don't want to use your full real name on this web sight. It's against the posting rules. Just thought you might want to know so you can reread them

.
Love,
Jamie