These days most employers would look first at achieving their aim by voluntary means. Much more straightforward with less likelihood of becoming embroiled in prolonged negotiations or industrial tribunals etc. Voluntary redundancy, early retirement, enhanced career breaks, unpaid leave are tools that are available before resorting to compulsion. When it comes to compulsory redundancy much depends on the industrial agreement between the employer and their employees, i.e. what the union and the company have thrashed out as the terms and conditions of service. In the majority of cases this will be based on Last In First Out (LIFO) although anti-age discrimination policy may now cast doubt on the absolute legality of this, hence the attraction of voluntary measures.
YS