Can I be made to take time off instead of payment for overtime?

No. When you work overtime, it is your choice whether you are paid or take time off.

Every now and again, we receive a call from an officer who states that a manager has requested overtime to be carried out saying that the budget has run out and there will be no paid overtime. If there is no budget then they can find someone else to deal with the job. The Police Regulations stipulate that you have a choice between payment and time off. If management refuse to pay you, they are breaking the law and render themselves liable to discipline. 

Remember that the time off is at the same rate as the overtime. If you have reckoned 6 units it becomes 8, meaning you can take two hours as Time Off In Lieu of overtime.