Can an employer require medical, or other, evidence before making a reasonable adjustment?
Often it will be be evident that the stammer is a ‘disability’, and that the employee is placed at a substantial (ie more than minor or trivial) disadvantage, so that the reasonable adjustment duty arises. Here there would seem to be no requirement for further evidence – though in practice the employee may well be willing to cooperate with an assessment by a speech therapist if the employer wants that.
If this is not evident, an employer may be able to argue in some cases that it did not know and could not reasonably be expected to know of the disability and/or substantial disadvantage, so that the ‘lack of knowledge’ defence applies. However at least if the claimant tells the employer he has a stammer and what effects (more than minor or trivial) it has on normal day-to-day activities, and tells the employer of the substantial disadvantage, it is likely the employer would struggle to establish a ‘lack of knowledge’ defence.
Cases where the ‘lack of knowledge’ defence is argued tend to be where the claimant has not clearly told the employer of the disability, and the disability was not otherwise evident.