They accept IGCSE or O Levels instead of IELTS as long as you have a C or better, the last time I checked. My offer didn't include IELTS as I had English O Level.
Depends on your O Level grades, and what subjects they were in. But AS Levels are more important (and A2 predictions of course, you need to have at least the minimum requirements as predictions to stand a chance, assuming you are applying after getting your AS results.), and the Personal Statement is also very important. A good PS can override bad O Level results.