Can people from non Russell Group unis make it in invesment banking?

Yes, success doesn't necessarily correlate to the university you first attended at 18/19.

Intuition, intelligence, character, confidence and a hint of luck can contribute to a person's success.

To discriminate against a candidate from a non-Russell group university could be potential suicide for a company - The wider the scope, the more choice an employer has.

Whilst this might all be true, it's not applicable as an answer to the OPs question. Investment banks are notorious for hiring most of their staff from a small pool of universities. When you have hundreds of applicants per role, you're not short on choice.

This is not to say you can't make it from a non-Russell group uni. You definitely can, there are no hard limits. This guys story is a little less applicable today, since now graduate recruitment is so commoditised and a greater number of people are going to university, so it's increasingly difficult to stand out. But he does demonstrate that just because you don't end up where you might want to be right out of university, that doesn't mean that you can't go there later in course of your career.

Of course it's possible, rare, but possible. You just have to work harder to prove yourself. If you have the right qualities and can put yourself in a position to demonstrate them, then you may be able to overcome going to a not a so good university and not having the network in place to get yourself in. University isn't the only factor, it helps obviously, but it is not a golden ticket.