Numbers for redundancy

Are the "20 or more" numbers based on compulsory redundancies, or should they include voluntary redundancies as well?

In other words, if we offered voluntary redundancy and 10 people accepted, which left us with 15 compulsory, would this be classed as individual (less than 20) or collective (20 or more)

A collective redundancy situation arises where an employer proposes to dismiss as redundant twenty or more employees at one establishment within a ninety-day period.

If you are proposing to make 20 or more compulsory redundancies this will also apply to “voluntary” redundancies if an employee has no real choice whether to stay or to leave.

If you as an employer are proposing to make say in the region of 20 to 50 redundancies (as per your question) and you are not sure whether there will be sufficient volunteers, or whether some of the redundancies can be avoided, then the obligation to consult employees and to notify the Department for Business, Enterprise and Regulatory Reform will apply.

Sorry that this isn't a black and white answer but I hope it's helped.