Yes there will be MUCH more maths on Warwick's MORSE than on LSE's maths+econ course, no doubt about that. With a four year MORSE degree you are effectively prepared to do research in a number of areas in mathematics, statistics, economics and finance. LSE's maths+econ can only really prepare you for further study in economics/quantitative economics.
Operational research is an interdisciplinary branch of applied mathematics and formal science that uses methods such as mathematical modeling, statistics, and algorithms to arrive at optimal or near optimal solutions to complex problems.
MORSE and Economics are both very strong courses at Warwick and entail good job prospects. Choosing one over the other based on "prestige" is not a good idea at all, you need to know which degree you are likely to be more interested in (and hence which degree you are likely to get better grades in).