UCL's Financial Mathematics have a good university reputation, but heard that (and indeed sure be true) they program structure is not at the same level of that one will expect from it's G5 status. A half-baked program. But if I were you I am likely to choose this one among your offers.
KCL and Edinburgh is the most mathematical amoung all those, of course i mean after Imperial. Good place for application for those with low IELTS.
Durham Fina and Investment shouldn't count as a FE/FM program.
St. Andrews is an famous traditional university, but as far as i remeber, their stat faculty is definitly not their strenght.