The thing is these days, a lot of people are more capable than ever before, of achieving those grades so good luck but just do your best and you'll be successful regardless..
Econ, Math, Further Math would be good for M.Sci. financial mathematics at Queen Mary leading on to a Ph.D. at LSE, KCL, UCL or Imperial and elsewhere so there's a good option for you as you will just as likely get a job in one the good investment banks and hedge funds.
Mathematics at Imperial is a 'target' course just like going for economics at LSE.
Have you thought about B.Sc. Mathematics with economics at LSE then M.Sc. financial mathematics then a Ph.D. at LSE or Imperial,UCL or Ox/Cam.
They will look at 3 grades as of the entry requirements.