To answer the OP - No.
What they care about is a) you have a 2i or First in a relevant subject(s) to your postgrad, b) that you have already shown you are very interested in this area, c) you have a 2i or First (with anything less you wont get funding), d) that you have two supportive references, and e) (for PhD) that your can write a solid research proposal explaining why all of this means you are the only person they could possible appoint.
Clearly if you are trying to go from London Met to Oxford then you've got a hard task (probably an impossible one), but non-RG to RG etc is totally feasible. Academics are not obsessed with league tables and rankings - just with 'is this the right person with the right background/enthusiasm'.
For employers, aside from a few up-themselves Merchant Banks and London Law Firms, most mainstream employers won't care either - if you have a 2i or a First, did more at Uni than just study (ie. an interesting, relevant CV) and can write a sensible job application, that is what they are looking for.