Non-compulsory redundancy covers voluntary redundancy.
You could ask employees if they would like to volunteer for redundancy and then select those to be made redundant.
Voluntary redundancy advantages
It is less demoralising and disruptive than compulsory redundancy and helps identify employees who are willing to accept redundancy.
Voluntary redundancy disadvantages
It could work out to be more expensive - you may need to offer enhanced redundancy payments to attract people to leave.
Management reserve the right to turn down offers from those volunteering to be made redundant.
There is also the risk that employees not granted their voluntary redundancy request may react negatively and you could also end up with an imbalance of skills and experience.