As you are 16, (assuming), you probably don't have a current account. You can open a current account with the Halifax/Bank of Scotland (same company now), called a cardcash account. You can do this online, the application takes very little time. It would give you a cheque book, debit card (visa electron) for online purchases and easy-to-use internet banking to allow you to do things like make bank transfers and keep track of your spending. If you are just making a one-off purchase then this probably isn't very useful but if you want to buy things online then it may be very useful indeed.
If you do opt to get that account, always remember that just because you can spend this money online, it doesn't mean you have to! I, as I'm sure many have, found myself buying lots of useless rubbish just because I could. Use it when you would save money on the highstreet but only if you were going to buy it anyway!