The legal position is stated here.
http://www.adviceguide.org.uk/index/life/emplo yment/bank_and_public_holidays.htm
It's kind of the other way around to what F30 says. The employer is not obliged to offer you the public holidays as non-working days, but your contract may say something that does entitle you to the time off. Then, as F30 says, if such a contractual element has in the past allowed for time-off, the employer (following consultation) could change that entitlement for 2009/10.
You could apply to take that day off, as part of your annual leave.