Chemistry gets a bit ridiculous -- even the AS stuff is pretty difficult (especially if you have no interest in Chemistry). Physics is certainly more difficult, but not to the magnitude of chemistry. Maths requires more practise due to the rigority of it, however that's compensated by the fact that it becomes significantly more interesting. Economics can get quite difficult in microeconomic theory of the firm due to the usage of graphs and graph relationships, but apart from that its progression of difficulty is much more 'natural' and manageable.
All-in-all, yeah -- it's quite a bit harder