Just to get the facts right...
The student loan will pay for all tuition fees and will cover living costs up to £4375 for students living with their parents, £5500 for most students and £7675 for students in London (these are all annual figures). The actual maximum size of the loan for living costs depends on the parents' income - the student will receive at least 65% of this figure but if the parents' income is below £62,500 they will get more. Tuition fees are covered in full regardless of the parents' income.
Students from households where the residual income (in broad terms this is income before tax but after pension contributions) is below £42,600 receive a grant of up to £3250 towards their living costs in addition to the loan, although the maximum loan is reduced a little. So if the household's residual income is less than £25,000 a student will receive a grant of £3250 and a loan of £3875 giving a total of £7125 towards their living costs assuming they are living away from home and studying outside London. The grant does not have to be repaid ever.
Students will NOT be paying the loan off for the rest of their lives. They won't pay anything unless their income is at least £21,000 per annum. The amount they pay depends entirely on how much they earn, not how much they owe. Any outstanding balance on the loan is written off after 30 years.
The net effect of the recent changes is that new graduates earning £21,000 or more will pay £540 per year less than under the old system. They will, however, be paying for longer and students on higher incomes will pay more in total, but students on lower incomes will pay less in total.
Student loans do not go on credit files unless the student defaults on the loan. Mortgage lenders say it will not affect students ability to get a mortgage, although it may reduce the amount they can borrow a little.
To all intents and purposes this is a graduate tax with a cap.
To answer the original question, how much you need to save depends on your income. If you earn over £62,500 per annum, for example, your child will only receive 65% of the maximum loan for living costs and will not be eligible for any grant, although their tuition fees will still be paid in full. You therefore need to think about saving enough to cover that gap.