Well,
after working my way through the MU120 mathematics preperatory materials and hearing that M263 is predominantly maths based course I have chosen to postpone M255 until Febraury. To be honest I know maths isn't necessarily my strongest point and to give myself the fairest chance of passing my courses to a good standard (M263 counts towards degree classification) I want to be able to dedicate all my time to M263 and MU120.

It was a bit of a relief to get it sorted, as the last 3 weeks I have spent alot of time worrying about my workload and the thought of my first two courses which contain final exams running directly in parallel. I hope I have made the right decision... time will tell though.