It doesn't actually matter how many hours a day you work. What we actually need to know to to be able to help you is how many hours per week a full-time employee works (i.e. 37 hours or what number?)
And we also need to know many much holiday (in days) a full-timer gets, and whether that includes the public holidays.
Go to the direct.gov.uk website and look under employment terms. You should get a minimum of 5.6 weeks paid holiday which may include bank holidays. Sounds as if you are being short-changed!
You are entitled to a minimum of 5.8 weeks per year(including bank hols)
If you contact ACAS they can give you advice on all aspects of employment law and are very helpful.
Seems like you're getting well short of that.
It isn't 5.8 weeks minimum - it is 5.6 weeks, as Trishy said. And you are definitely being short-changed, because as an absolute minimum, you should be getting (30*5.6) hours holiday per year - which is 168 hours holiday per year.
However if your employer doles out more than the statutory minimum to full-time employees, you would be entitled to more than that - which is precisely why I asked the question I did.
Without an answer to that, I can't help you futher.