I recently got biro on my leather sofa and my cousin suggested hairspray. it did work. try spraying some somewhere you cant see it first though and just dab it rather than rubbing it. good luck!!!
you can get something from the supermarkets,i think flash do it,specifically for that it is like a giant rubber/eraser that you just rub off the marks ,my friend tried it a few years back when she had the same problem and she said it was brilliant , i can't remember what it was called though,so to be so vague