Your rights in the workplace depend on your age (table below)

-14 year olds
There are a lot of rules that control working hours of children, but the basic ones are:

during term time, you can only work for two hours on weekdays and Sundays and for five hours on Saturdays
during a school holiday, you can work for up to five hours on a week day or a Saturday and no more than two hours on a Sunday
you cannot work before 7 am or after 7 pm
-15 and 16 year olds
If you're 15 or 16 and are working while you're still at school, your rights are almost identical to those of 14 year olds. However, you are allowed to work for up to eight hours on Saturdays or during the school holidays.

-16 and 17 year olds
If you're no longer at school and you're 16 or 17, the law refers to you as a young worker. Because you will no longer be at school, there are fewer restrictions on when you can work and for how long, but there are still some rules.

You'll only be able to work for eight hours every day, or a total of 40 hours over the course of a week. You cannot usually work an overnight shift either, but there are some exceptional circumstances where you can.

Because you've reached school leaving age, you may find that employers may be more willing to offer you part-time or full-time employment. You're also not limited to just 'light work', so you'll be allowed to work in places like a busy shop, restaurant kitchen or as a waiter or waitress.