As i understand it, your managers can in fact set out your hours (37.5) in any way shape or form and this could include weekends or Public Holidays! The latter would be compensated for with a day off in leiu.(AFC Para 13 Annual Leave & PH policy)
AfC para 13 actually says that if you are working or on call then you get an equivalent time off in lieu. Therefore if you work 12hours then you get 12 hours off in lieu and if you are on call for 24 hours then you get 24 hours off in lieu.