Eighteen months and two cases on, the age discrimination laws are a mess. Lawyers are crying out for authoritative guidance on how they affect their own profession. Managing partners cannot afford to bury their heads in the sand: they must act now to minimise the risk of being sued.

Since October 2006, discrimination in the workplace on the grounds of age has been illegal unless it can be “objectively justified as a proportionate means of achieving a legitimate aim”. In other words, you can treat people less favourably purely on the grounds of their age as long it helps the business to overcome a genuine obstacle.

The issue that has kept lawyers guessing since the legislation was introduced is what constitutes a “proportionate" – a vague term undefined in statute and left to the courts to clarify.

Ironically, while lawyers have been busy advising their clients in other sectors about how to keep on side of the regulations, they have been struggling to grasp what they mean for their own profession.

With age discrimination laws in effect, individual law firms must decide whether partners should be subject to a mandatory retirement age and if so, what age it should be. These specifications are set out in the partnership deed, a legal document governing the way a particular partnership works that all partners must sign.

The law is clear that an arbitrary partnership retirement age - whether 55, 60 or 90 – is unlawful unless it satisfies the test of being a proportionate means of achieving a legitimate aim. The crucial question according to Ronnie Fox, principal of Fox Solicitors, is what firms can and cannot justify under this test.

But with only two cases involving partners suing their firms having come before employment tribunals so far, lawyers say there is a dire shortage of authoritative guidance necessary for other firms to solve the issue confidently.

This problem is exacerbated, they say, because the first case - in which Peter Bloxham, a former head of restructuring at Freshfields Bruckhaus Deringer, sued the firm for age discrimination - focused on a very specific set of circumstances relating to changes in the firm’s pension scheme.

The second case – Leslie Seldon v Clarkson Wright and Jakes (CWJ) – is potentially more relevant because Seldon sued CWJ for forcing him to retire at 65 (the firm’s predetermined age) by directly challenging the firm’s partnership deed.

However, as with Bloxham, the case turned on specific facts. The tribunal was careful to point out that the Seldon judgment should not necessarily be seen as a blueprint for other firms, especially those larger than CWJ’s 10-man partnership.

Anthony Fincham of CMS Cameron McKenna says: “Bloxham and Seldon are two fact specific cases decided in an employment tribunal whose rulings are not binding. What we need is some authoritative and binding guidance from the Employment Appeal Tribunal or the Court of Appeal on the key points of age discrimination.”

Fincham adds: “At the moment, the picture is no clearer than when the regulations were first produced.”

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