Your statutory holiday entitlement used to be 4 times the number of days you work each week. (So you'd get 20 days per year).
From the 1st October 2007, that entitlement went up to 4.8 times the number of days you work each week.
If you were employed throughout the whole of 2007, for 5 days per week, your statutory holiday entitlement for that year was 21 days. (That's because three quarters of the year was under the old rules, with the final 3 months under the new rules).
During 2008, you're entitled to 24 days paid holiday.
The rules change again, from 1st April 2009. The multiplier will then be 5.6, instead of 4.8.
Because 2009 comes under different rules for the first 3 months to the final 9 months, you'll be entitled to 27 days holiday in 2009.
From 2010 onwards, you'll be entitled to 28 days paid holiday.
When calculating your holiday entitlement, remember that any days when the firm is closed for business (e.g. Christmas Day) are included in your statutory holidays.
Public holidays have no special significance under employment law. If you'd normally be working when a public holiday occurs, your employer can expect you to work as usual, without any additional pay or time off in lieu (unless, of course, your contract specifies otherwise).
See here:
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/DG_10029788
Chris