Mr Lewis warned graduates who clear their student debt quickly may end up paying more than they need to.
Here we explain the repayment options.
Option 1: pay off the loan upfront
The benefit... The main advantage is that students are debt-free.
Student loans do not show up on your credit file, so they are unlikely to impact the ability of graduates to borrow in future. But lenders do take them into account when considering mortgage applications.
"Having a student loan is worse than not having one when it comes to getting a mortgage, " Mr Lewis said. "Though going to university often results in earning a higher salary, which usually cancels this out easily."
The catch... This option could leave graduates tens of thousands of pounds worse off in the long run.
This is because, as any remaining debt is wiped after 30 years, graduates may be paying for sums they would not otherwise be liable for.
Almost three quarters of students completing their studies will never repay all of the money borrowed under the post-2012 funding system, according to predictions.
"With £9, 000-a-year tuition fees now a reality, many parents are desperate to build uni funds to protect kids from huge debts, " Mr Lewis said. "But this laudable aim could be throwing away over £20, 000."
Option 2: make the minimum required repayments
As long as graduates earn at least £21, 000 a year, they will repay 9pc of their income above this sum, with repayments staggered according to earnings.
The benefit... Lower earners are required to repay little or nothing at all, although do not avoid interest being added to the sum owed.
Only higher earners will be shelling out large amounts (see table below for a guideline to monthly repayments).
£9, 000-a-year fees: how much will graduates repay?
|Annual salary (gross)
||Monthly salary (gross)
||Monthly loan repayment
|Less than £21, 000
||Less than £1, 750
Source: Student Loans Company
The catch... Student loans still attract interest (currently 5.5pc) so slow repayments could end up costing more.
As long as you owe money, interest will be "compounded", that is, added to the total amount owed each month.
The interest graduates repay is calculated based on the Retail Prices Index (RPI) measure of inflation from the previous March plus 3pc. So for 2014 to 2015, the interest is 5.5pc.
Interest is added during your studies as well as after graduation.
Graduates earning less than £21, 000 escape repayments but are still charged interest equivalent to RPI (2.5pc for 2014).
Option 3: 'overpay' the loan using extra cash
Graduates can also make voluntary payments to the Student Loans Company to reduce the debt earlier.
The benefit... This has the potential to reduce the amount of interest paid on the total loan - but also means it is less likely for any debt to be "written off" after the 30-year period.
High earners may be better off overpaying. This is because those earning, say, £40, 000 a year for the next 30 years are likely to pay off the capital of amount borrowed. By paying off the loan more quickly, they will incur less interest.
The catch... As already mentioned, paying off a student loan as quickly as possible may be a bad decision as many people won't need to fully repay their debt.
Even those on high salaries in their 20s or 30s cannot guarantee they will consistently be earning a high salary for the next 30 years. If their earnings fall, part of the loan could be written off in the future.