Marketing university entry requirements

Hi, I've been looking at universities for marketing in London like City and Queen Mary who want a 6/B for maths. Those universities are at the top of their courses. Most unis for marketing ask for a 6/B would they still accept me with my 5 or will it be difficult even after I graduate to get a job? Is my 5 in maths holding me back even if my other GCSE grades are better?