If you are financially able to repay your loan early you can. But do not do do if you have any other debts that you are paying interest on at a higher rate.
If you intermittently have extra cash, put it in an ISA and you can either pay the interest you earn to help overpay your student loan or wait until you have put aside enough to pay the balance of your loan. If not having debt, even a benign student loan type gives you peace of mind, the repay it early if you can afford it.
Check what the interest rate is going to be for the year, they review it every March and implement the increase in September. If you are on the pre 2012 student loan repayment, then Bank Base Interest rate is used to set the interest rate, it is currently 1.5% but could go up in future substantially if the economy improves. If you are paying loans under the post 2012 rules, your interest will be tied to the inflation rate plus up to 3% in you earn 21k - 40k. So if inflation goes up substantially, your outstanding loan will grow faster. I think if you earn less than 21k and have surplus income and know that you will earn in excess of 40k in the future there is a case for making voluntary one off payments to reduce your loan. This is because you only get charged the rate of inflation as interest. If you are on track to earn more than 40k, you will likely not benefit from the loan being written off after 30 years.
If you get your loan statement and you work out that there is less than 12 repayments left, if you have the funds, then that is a good reason to repay the outstanding amount in a lump sum. This is because your tax code will be set for the year, student loan company only tell the HMRC at the end of tax year to stop collecting loan repayment. So if you clear the loan after the 1st month payment from your salary, you may make another 11 unnecessary payments. Which you will have to reclaim from the student loan company. You might not pick up on this overpayment until you get annual statement.