It would be useful to add a new function to Report Designer and Generic Inquiry that will calculate the difference between 2 days excluding weekends and bank holidays.
For example, date 1 is 02/07/2018 and date 2 is 17/07/2018.
If a datediff function is used, then the result will be 16.
04/07/2018 is public holiday.
06/07/2018, 07/07/2018, 13/07/2018, 14/07/2018 are weekends.
If public holidays and weekends are excluded, the result will be 11 (16-5).
The list of public holidays can be used from Work Calendars screen.