I'm going to cut and paste from a thread from a couple of days ago about bank holidays and calculating part time entitlement -
In terms of pro rating them, as a part timer you can't be disadvantaged when compared to a full timer.
For 'normal' 5 day weeks I usually advise managers of part timers to divide 8 by 5 then multiply by the number of days the part timer works each week. Then look at the calendar and see how many bank holidays will naturally fall on the part timer's working days - this will vary depending on the days the person works and when Christmas and New Year fall.
Then the part timer may have days to make up or extra days to take.
-------
So if there are 8 bank holidays for people who work 5 days a week, and you work 4, you will be entitled to 5 of them. You should look at your calendar each year, see how many of the normal bank holidays fall on your working days, and make an adjustment up or down appropriately to the number of days you work.
You have no automatic entitlement to bank holidays, you have a right to 4.8 weeks off work, which can include bank holidays, and you have a right not to be disadvantaged compared to a full timer at your place of work.