Suppose an employee suffers an episode of depression which in her eyes is due to “stress at work” i.e. overwork and lack of resources. Unfortunately this is not uncommon. It is unlikely that the employer will be liable either under the common law or under disability discrimination law unless the employer was put on notice that disaster was imminent: Hatton v Sutherland [202] ICR 613.

But suppose further that many months later she comes back to work. At this point the employer is at legal risk: it knows that the employee’s mental health is at risk and so the common law duty of care obliges the employer to take reasonable step to prevent further injury. As a matter of employment law, the employee is probably disabled and the employer certainly knows that this is so. Accordingly the duty of reasonable adjustments requires any workplace practices which might disadvantage the disabled employee to be adjusted.

If the employer fails to carry out its duty of care/reasonable adjustments, the employee may break down again. If so, the employer will be held liable for failing to deal properly with the return to work.

Now comes the question: suppose the employee’s loss of income over the next 5 years (to retirement) is £200,000.  What is the employer’s liability?

The legal problem is that the loss is arguably not caused solely by the employer’s failings with respect to the return to work. It is also caused by a pre-existing vulnerability arising from the first episode for which the employer is not liable. Does this mean that the full liability is to be reduced or “apportioned between the wrongful and non-wrongful causes of the loss”? The answer is important because it might reduce the compensation in our case from £200,000 to £100,000 or even less.

Currently the answer is not clear: in Thaine v London School of Economics [2010] ICR 1422, the EAT held in favour of apportionment.  However, Dame Janet Smith, both in her capacity as a judge of the Court of Appeal (Dickens  v O2 PLC) and extra judicially (in the 2008 Munkman Lecture), argued for a negative answer on the grounds that the there is no rational method of separating out the different causes of the loss. There is also the argument that because the employee has a pre-existing vulnerability, the employer must take the employee as it finds her. Finally, it can be said that the whole point of the Duty to make reasonable adjustments is to accommodate those known to be vulnerable – so that it follows that responsibility for the consequences of breach cannot be avoid by pointing to that very vulnerability.

In the recent case of BAE v. Konczak [2014] the EAT held that it was open to an ET to find that there is no rational method of separating out the different causes of the loss i.e. that the loss was “indivisible”.

This does not seem satisfactory: whether compensation is to be reduced in this way is a question of principle which needs to be determined by the Court of Appeal.