Contra what is being said by the big beasts, I think that there is a pretty well definitive answer to the question "is either Warwick or the LSE better regarded than Imperial either domestically or internationally" and that the answer is "no". I think there is no need to contextualize here just because areas of overlap are so few.
Saying "well, the LSE is better regarded for politics" isn't sensibly contextualising the question. It's doing the opposite.
With UCL subbed in for Imperial, we could be here all night, but with these two it only boils down to the asking of two questions:
Warwick Maths > Imperial Maths? No, not really, 'bout the same.
LSE Msc Finance > Imperial MSc Finance? Likely not to the extent that it makes any difference.
And then that's it.