holidays

reading on a directed site from here , i was intrigued to see that our company is entitled to pay us 28 days holiday as of last October 2007,because we allegedly work a 6 day week.
We do however get 28 days, but it has only recently been updated.
We are in an akward situation because our contract of employment states that we must work a 5 and a half day week, whereas what we actually do is a 6 day week followed by a 5 day week. Now i know it averages out at 5.5 days a week, but it has also let them off the hook when it comes to paying the holiday entitlement, cos the way i work it out, they owe us holiday since last year…