This may help.
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/DG_10029788
You are entitled to the statutory minimum or whatever your contractual terms state. The higher of teh two provisions will apply.
The current minimum is 4.8 weeks (including bank holidays) but this will rise to 5.6 weeks (including bank hols) from April 2009. It's probably easier to convert it to hours. For you that's 5.6 weeks @48 hours a week. That will be 268.8 hours a year. Or , to put it another way, 5.6 weeks @ 4 shifts a week means 22.4 shifts off as holidays.