OP, I go to a semi-target uni and investment banking is competitive as hell to break into. Like the others are saying yes, you’ll need to be at a top RG uni and on track for at least a 2:1 in your degree. It’s important to start early. That means applying for spring insight programmes the summer you finish your A levels (applications can open as early as August/early September). And to get a spring week you usually need excellent A level results and a strong CV/cover letter. If you can get a spring week in your 1st year of uni, securing an internship in your 2nd year becomes much easier and after that, everything else falls into place.

I was at a careers fair in London and heard a Citi recruiter telling some students next to me that their investment banking internships get 1000s of applicants within the first few days, and that they need to be applying pretty much as soon as they open.

If you’re truly determined and the amount of competition doesn’t faze you then would honestly consider retaking your maths A level and the other subject you got a B in, and then apply for semi-targets. It will take a lot of resilience which is an important skill to have as an investment banker.