A common myth is that student loans directly damage your credit score. They do not. However, they significantly impact your mortgage affordability calculation.
The Affordability Test
Lenders deduct your monthly student loan repayment from your gross income before calculating how much you can borrow. With Plan 5 loans requiring repayments at a lower income threshold, many first-time buyers are finding their maximum borrowing amount reduced.
What You Can Do
Do not overpay your student loan just to get a mortgage. Instead, focus on reducing commercial debt (credit cards, personal loans) which lenders view much more negatively.