Interest is charged on your student finance debt. This is compound interest, which means that interest is also calculated over the interest itself.
In 2016, the annual interest rate is 0.01% (in 2017: 0.00%). The interest is charged from the month after the month in which the student finance is credited to your account. As long as you follow a degree programme and qualify for student finance, the interest rate will be determined by the government every calendar year. As soon as you stop your programme, the interest rate will be set for successive 5-year periods.