Yes, that is right - a minimum of 5.6 weeks paid leave per year. This may include the 8 public holidays. So that's 28 days for a 5-day per week person, and pro rata if you work less.
It gets messy if you work a different number of hours per day, and the ONLY way to correctly calcualate your holiday in such circumstances is in holiday HOURS.
For you, I would assert to your manager that you are entitled to 2x5.6x8 HOURS holiday per year, which is 89.6 hours per year.
The bit that bothers me is that you say you work an average of 16 hours per week. You manager may well claim that he reckons you are a casual employee. I don't think that you are in those circumstances.
Read about that here:
http://www.direct.gov...femployment/DG_183496
The main link about holiday entitlement is at this link:
http://www.direct.gov...dholidays/DG_10029788