The answer, which you can derive also by looking at Factor's good link, is that you are entitled to a minimum of 5.6 multiplied by 30 HOURS in annual holiday (168 hours), if you are contracted for 30 hours per week.
We can't tell you how many days that is, partly because you didn't tell us how many contracted hours a FULL-TIME worker does. This makes a difference, because if you are working 30/40ths (three-quarters) of a full-timer's week, you would be entitled to less holiday allowance (as a statutory minimum) than if a full-timer in your organisation works a 35 hour week, whence you would get 30/35ths of that amount - a bigger slice. All these figures include public holidays, by the way.
Working more than 30 hours in some weeks doesn't change your allowance - it is based on your CONTRACTUAL hours - a source of much anguish for some people because unscrupulous employers exploit this loophole by keeping an employee's contracted hours down, allowing them to work overtime at non-enhance labour rates - denying them the holiday otherwise accruing.