I work at one of these funds in the UK. The majority of our quants -- and, indeed, our front office engineers working on the trading stack -- are Oxbridge grads.

If you want to be a quant, getting a post-graduate education at a top-tier university is pretty much a requirement. If you want to be a software engineer/SRE/etc. in the front office, you might be able to find your way in by going to the tech industry proper and then pivoting.