It is completely feasible to agree a temporary trial of a flexible working arrangement. And if the employee is compliant there's no reason you can't just keep reviewing it every three months. But the fact is that, once you're six months in, if the employer cannot demonstrate an impact on quality or performance, the employee would be perfectly entitled to insist on the arrangement being made contractual.

At that point the question must inevitably be "so what?" Are you a public sector or unionized employer? If so, you can expect legal challenges to follow if you fail to comply with the regulations. If not, you probably have more leeway but should be aware that the employee could take the issue to Acas and to an ET, or resign and claim constructive unfair dismissal if they have qualifying service.

In reply to Robey:

Thanks Robey. It's Public sector and I am already anticipating having to explain to the relevant manager about why we would not have much of a defence if productivity and general employee morale improves (as I suspect it will). The rationale for the proposal is based on a lengthy commute. It could be argued that the EE joined knowing that the commute was a reality, but retention of a key EE is an issue here so I think we need to be sensible. I suspect that the manager's position is based on an outdated and possibly untrusting view of wfh. I think I will advise that we could put it in place as suggested, but that we should be prepared to accept a permanent change if the employee pushes. Thank you again for coming back so promptly.