Hi paddlechick
Was convinced I'd answered something like this fairly recently, so did a search and found the below answer which I've cut and pasted rather than write it all out again as I have DS in one hand!
"You get pro rata the same number of bank holidays as a f/t member of staff.
So, for example if someone works 3 days a week, Wed- Fri, they would be entitled to 3/5 the bank holiday entitlement of a f/t member of staff. F/t entitlement is usually 8 days, in England anyway, so a 3-day a weeker is entitled to 4.8 days, which I would round up to 5 (following me so far? ).
What I have done in organisations I have worked for is got p/t members of staff to sit down with their manager at the beginning of the year and work out which bank holidays naturally fall on their working days, and then adjust.
So if a part timer works 3 days and is entitled to 5 bank holidays, the manager would look at the calendar at the beginning of each year to see how many would automatically fall on working days - this might change each year as obviously Christmas, Boxing Day and New Years Day vary each year.
If the number of days that fell naturally on the p/t persons normal days was less than 5, the manager would ensure they took a day in lieu to make it up, usually in the same week as a bank holiday."
I hope that makes sense, seems a bit complicated!