Im just highlighting a few points for the sake of arguing here tbh... the above post by delta is a fair conclusion tbh..
The answers pretty simple... Take 100 people with degrees and 100 without. The ones with degrees will earn more on average.
problem with that is that amongst the non grads youve got people who couldnt have gone to uni anyway (cleaners, builders etc..) - if it was possible to compare non grads who could have gone to uni but didnt vs grads then youd probably end up with a lot less of a gap. Though yes there probably still would be a gap.
Noone you meat now of the late 20s starting out in the city is without a degree/graduate scheme or a close friend who introduced them. The point is you cant compare people you currently see in professions to those being employed from this generations output.
Yes you wont get on a grad scheme at an IB without a degree - in fact these days a mere degree isnt enough - youd be hard pushed to get on one without straight As at A-Level, a couple of summer internships in investment banks and a 1st or 2.1 from a top uni. When they are offering 35k per year starting salarys for new grads they can afford to be fussy.
Having said that non grads arent confined to taking a job in the back office and then working their way up - if you really use your initiative and can sell yourself well then some stockbroking firms do still give junior broker positions to non grads.
Theres a simple response to people like Richard Branson examples... A bank would be very unwilling to give you a business loan to get going without a degree so its getting very hard to reproduce.
If someone is stopped from going into business by being turned down for a bank loan then they probably dont have the potential to be the next richard branson anyway.