Thank you very much for your advice, perhaps I could give more context. Although I know it is a rare route, I intend to apply for the mentioned universities in Autumn 2014, after I finish my A-levels. My teachers are not willing to give me the necessary predicted grades to make a competitive application. I have however got assurances from university tutors that if I do get A*A*A grades with distinction in STEP I and II, I will get an interview. That's motivation, if I ever needed it!
My C was in chemistry which I was certainly surprised by; at the very least, I have a sense of shame and disbelief that the work and effort I put in for the subject didn't come to any thing.
But more importantly, please correct me if not, doing 5 subjects to AS is not uncommon for Oxbridge/LSE/Imperial applicants. It hopefully demonstrates to admission tutors that I am hard working, and can mange the workloads of undergraduate study. That said, I clearly didn't manage it that well last year, though I am more organised, focused and determined now.
I am worried about the potential number of exams that I would have to do next summer. Here is a crude estimate: Econ A2 (2), Phys A2 (2), FMaths A2 (6), Chemistry AS (2), Further Maths AS (3). This will be difficult to undertake. Part of my problem this year was managing my time for the 13 exams I had to do. This year there could be as many as 15!
As always, any advice or insight is much appreciated