Last year, the Supreme Court remitted his claim back to the employment tribunal, to consider a number of issues relating to justification (the main one being whether 65 was an appropriate age for mandatory retirment, or whether another age such as 68 or 70 should have been adopted).
The employment tribunal has, this week, found in favour of Clarkson Wright & Jakes. In its written reasons, the tribunal held that retention and planning were legitimate aims, that collegiality was also (with some caveats) a legitimate aim, and that a mandatory retirement age achieved these three aims. Importantly, it held that a mandatory retirement of 65 was a proportionate means of achieving those aims (see paragraphs 79-81 of the reasons). Accordingly Mr Seldon lost.
Note that this is not a panacea for companies to justify a mandatory retirement age of 65. First, justification will always depend on fact-sensitive matters relating to the particular employer. Second, this case was decided based on social policy and demographics in 2006, before the abolition of the national retirement age. Societal norms about people working beyond 65 have moved on in the last seven years, and the tribunal specifically stated that the case might be decided differently on facts arising today (para 92).