Can you spot the slight problem with this league table? I'm amazed they put this out when they got the results.
To any university not scoring highly on social mobility, all they have to do is move to London. Where they'll get a load of high achieving poor students who will live at home (saving them money on accommodation) and have a good job market to move into. Whatever you do, don't get stuck with provincial poor kids who won't have good local jobs available, and won't be able to afford to move to London.
I assume that Aston and Bradford get lots of poor kids who live at home, but fall down by only having poor cities nearby for them to get jobs in afterwards. The third and last entry from outside London is Hertfordshire. They have access to London jobs, and probably some poor kids from Hatfield and Stevenage, but not enough of them. Move to London, chaps.
I'd venture all this tells you not very much about the quality of the HE institution. It's sort of amusing, but there's the danger it'll be used as an excuse to shit on universities in Sunderland, Huddersfield, Wolverhampton etc.