This depends on how generous your employment contract is. Most employers will let you have the following Monday off if, say, Christmas Day falls on a weekend. However, as there is no general legal right to time off on bank or public holidays (though it is a common practice), there is also no legal right for you to transfer the day's leave to another day, if it isn't mentioned in your contract.
You should check your staff handbook, and discuss this with your employer, but be aware that if your contract does not specify otherwise, your employer's decision on this may be final.
