Cherist.
For some careers (law being a v important one) and actually for anything in the city, firms are only recruiting from top universities.
I'm not talking about when I was hired (12+ yrs), but now. It is almost impossible to get a training contract if you went to an ex poly. Sorry -but it is. I work with a lot of paralegals who are almost all ex-poly and cannot get interviews, let alone jobs. There are just too many candidates with "better" institutions on their CV.
I chose to go to a top ranked university (yes, RG), and do a different course - not law - then converted to law later. I wouldn't have got in to study law. However people still comment positively on my university when talking about my background. And choosing this two stage process is something I would recommend my DC did in the future.
A 2:1 from East London University just does not measure up to a 2:1 from Kings.
My current employer (finance not law) ONLY hires from Oxbridge/LBS.
It does happen, and to think it doesn't is naive.
I'm not in anyway saying you can't get A job with a degree from a lower ranked university, just that some fields will be barred to you. However like other posters have said, some fields positively LOVE ex-polys, due to a specialism etc etc etc. You have to know what it is you ultimately want to do. if you don't, you are better off picking a top ranked uni as this will stand you in better stead in the future.
Oh and as for Sussex, certain courses are outstanding - their chemistry department for example has much to recommend it, not least the Nobel prize of Sir Harry Kroto.