As others have said, if you are working compressed hours (ie a full week in 4 days rather than 5) you should be entitled to the normal number of holdays, ie the 24 you quoted.
You are also entitled to the 8 bank holiday days, therefore your entitlement is 32 days in total.
As others have said, you then need to convert the 32 days into hours and then consume them in line with the hours you are actually working. IE if a compressed day is 10hrs, a day's holiday debits you 10hrs from your entitlement.
If a bank holiday falls on a work day you must use up your holidays to cover it. If your day off is a bank holiday you do nothing as you wouldn't have been working anyway.