Seriously, bumped after 5 hours?
I'd say if you really wanted to study Maths and Econ, the best place to do it probably is LSE. Warwick has the stronger Maths department, whilst LSE has the stronger Economics department.
The MORSE degree itself has very little Economics (as far as I know) - although you could change that with what your options.
Employment prospects would be strong for either I imagine - although I think LSE may have the edge because of the name.