Ok a hypothetical situation based on a true event at school.
Person A lives at home with his mother, who last year started a new business, this therefore reduced her income to below £5000. However his other parent still earns a very respectable wage that would have put them into a much higher bracket of the loan system. However, as things stand his dad's details arent asked for, as he doesnt live at home. Yet he fully contributes to the family and the fees.
So he gets maximum loan, maximum grant and maximum university support. Which may come to over £6000, without family contribution. Pays lowest course fees.
Person B has two parents who both earn reasonable salaries (say 15k and 20k) - Thus putting them in a high income bracket. As both parents live at home, both details were required. With the combined incomes that may well total less than person A's dad's income, they a higher percentage of the fees, and receive a lower percentage of the loan.
There is obviously no sense to this system, especially in this hypothetical example. But it would be incredibly difficult for the university to asses individually each one of the thousands of applicants to university each year. Especially if they need to take into account parents roles within the family and disposable income.
There are winners and losers, but I don't think thats good enough.