If an employee is working full time hours (37.5) in 4.5 days (rather then 5 days) should their holiday entitlement be reduced ?

I.e. -  on 37.5 hours / 5 days (7.5 hours per day) entitlement is 28 days including bank holidays , if the employee is still working his contacted full time hours but with longer days are they still entitled to the same holiday allowance ?