I'm thinking of this in the context of the current debate about coronavirus vaccine certificates, but I think the question is wider and I don't want to limit it to just that.
Suppose an existing long term employee develops some trait or condition, that means they now pose a risk to others.
It could be a neurological injury issue - they uncontrollably say offensive things (racist comments, threats, obscenities), they become unable to reasonably assess dangerous or risky conduct as they do their daily work (risk of injury through carelessness/impulsivity/damage to perceptual senses). It could be a mental health issue that lacks control or where they refuse meds due to religious beliefs or clinical vulnerability (real or self imagined). It could be that they present a medical risk via contagion, that in the circumstances no tests available to the employer can adequately mitigate.
Perhaps it can be mitigated by some action of the employee, but such action would be of a kind an employer can't reasonably demand, such as relevant medical intervention, therapy, or some kind of change to lifestyle/domestic circumstances (therapeutic exercise, physical aids). Or perhaps it can't be greatly mitigated at all.
Assuming one could not reach a finding that either employer or employee were acting blatantly unreasonably.....
What is the position in UK employment law, of an employer who finds that despite best efforts they can neither mitigate the risk to a comfortable/safe level, nor find an alternative role or accommodation that is workable for the employee? (Note that I'm not assuming a big employer, the question would be as pertinent for a 10 person business as a 10,000 employee one)
Can they be removed from work on safety grounds, if no prior contractual condition covers the situation?
Is the situation any different if there are mitigations available (say medications to take an extreme!), but the employee for personal reasons states they simply don't want to do them and the employer can't force them to do so?