Have had a thought on this one and am a little surprised there's not been much talk about Imperial, after all it is part of COWI.
The reason is that for a university as a whole, I think it has more prestige than Warwick but for maths Warwick would be more prestigious.
However, for an 18 year old who does not know whether or not they'll do well at uni, they should choose the one that will open more doors for them at the end of it.
Suppose choose Warwick and do well, then
can continue in academia (at Warwick or anywhere else) or get job in real world.
If academia, Warwick will open doors else job, Warwick opens fewer doors (than Imperial)
if not do well then job and again Warwick opens fewer doors (than Imperial)
On the other hand, if choose Imperial and do well, then
can continue in academia (at Imperial or anywhere else) or get job.
If academia, Imperial will open doors but not as many as Warwick
else job, Imperial opens more doors (than Warwick)
if not do well then job and Imperial again opens more doors (tha Warwick)
The critical point is that if one chooses to remain in academia, academics will know about both Imperial and Warwick, with Warwick given an edge.
However outside of academia, Imperial would have a bigger edge, especially in the Far East.
Like to hear Warwick / Imperial students / grads view.