Investment Banking CV - Too many achievements at university

That's rubbish. I'm 19 and have spoken to various HE, recruitment and other figures about it and they all tell me two pages is fine for a CV.

I have been offered jobs with John Lewis Partnership, BP, Shell and various other companies who have all found my CV to be fine.

If you haven't worked or have only worked one job then maybe. But if you've worked a couple of positions (particularly with quite a bit of responsibility), have a lot of academia and achievements then two pages is fine.

Beyond two pages is a bit much unless you're potentially going for a director position. They don't want your memoirs.