Mocks do not mean s***. The teachers mark horrendously harshly in an attempt to "scare" you into revising harder and also act as if you don't have a massive 5 week (or however long it is) study leave where you actually bother to work a bit. I got some As, Bs and Cs in my mocks and at parents evening had a teacher telling my mum that unless I worked incredibly hard I was destined for a C in chemistry and then hey, what happened.... They mark ridiculously nicely in comparison to our teachers in the real thing so I came out with 7 A*s 3As. Mocks are bs.