Last-in, first-out uses length of service to select employees for redundancy, starting with the most recently employed. It can be transparent but does not tell the whole story about the skills needed in the remaining jobs.
There is no blanket prohibition on LIFO, whether used alone or as part of a wider matrix. Its fairness depends on the situation: the choice of pool, any agreement with representatives, the employer's aims, how service is measured, consultation and the impact on affected people. Acas generally recommends objective, measurable selection criteria such as skills, documented performance, attendance (excluding relevant protected absences) and disciplinary record, applied consistently. A single service-only criterion may be harder to justify in some circumstances, but is not automatically unfair.
Length of service may disadvantage younger workers as a group. Indirect age discrimination requires analysis of the actual disadvantage and whether the criterion is a proportionate means of achieving a legitimate aim. It cannot be established just by comparing one younger employee with one older colleague. Even adding other criteria does not automatically cure discrimination; the weighting and evidence matter. Age discrimination claims are not capped in the way ordinary unfair dismissal compensatory awards generally are, but compensation is not guaranteed.
Ask in writing for the selection pool, criteria, weightings and your scoring. Ask why service was used and whether skills and remaining business needs were considered. Compare available evidence fairly; do not assume an employer must hand over unrestricted personal information about colleagues. Raise specific errors in consultation or appeal, and seek employment advice if age-related disadvantage is a concern. A valid settlement agreement waiving claims requires independent advice, though the employer is not generally obliged to pay your adviser. In Great Britain, do not let appeals or negotiations run past tribunal deadlines; contact Acas about early conciliation. Northern Ireland has separate law and LRA procedures.
Resources: https://myredundancyrights.co.uk/action-plan and https://myredundancyrights.co.uk/calculator