Incapacity to do the job - on medical or any other grounds - is a potentially fair reason for dismissal. In theory it is therefore possible to dismiss an employee fairly on this ground, but only if you follow the appropriate procedure.
However, this is not the only consideration. It is possible that the salesman would be regarded as disabled for the purposes of the Disability Discrimination Act 1995. If so, you would be legally obliged to carry out an assessment as to whether any reasonable adjustments could be made, to ensure that he was not placed at a disadvantage.
There are other factors to consider, such as the effects of dismissal on any entitlement to receive benefits under a permanent health scheme.
In view of the very substantial compensation that can be awarded to employees unfairly dismissed in such cases, it will pay to obtain legal advice before taking any decision to dismiss.
