I am at Southampton university which like Bristol is one of the best in the country for enigneering and in our first year maths I dont think they really assumed any prior knowledge above AS levle standard. So in that respect further maths is not neccisery at all, you will find yourself covering that matireal in your second semester of first year. Having done it already will make that module easy for you and mean that you probably go away with it more secure inside your memory since you have covered it more times. You will also learn things we do not learn at university since at university you only have time to learn what is the most relivant to engineering, ie calculus, vectors, transforms, matrices and not much else. Chances are that wheather or not you take further maths, it wont make a very big diffrence to you.