You cannot unilaterally impose the change. You must discuss and formally agree any changes to these substantive terms.

In reply to Ray:

Thank you Ray. I assume we also have to be careful about the employee going through the menopause...isn't it an adjustment to allow flexible start and end times?

In reply to Clarky:

The menopause is not necessarily a disability, it might be and being flexible cuts both ways.

Flexible working requests are the right of an employee, and the employer must consider any reasonable adjustments to accommodate such a request. An employer does not have the benefit of a similar right...... it’s a one way street. So unless the employee actually requests to work later hours, your only option is discussion, negotiation and joint agreement.

It doesn't feel like demanding an employee changes their normal work pattern is going to be in your best interests here, legally or pragmatically. Good discussion with the person involved, particularly around her reasons, will be your best way forwards. If she has said that working later in the day affects her focus/concentration, then it seems that she's being thoughtful about the best way to do her best work for you (and really is it in your interests to have work done later if it's more likely to have mistakes in?).

Hopefully her thoughtfulness on this is a good basis on which to have a constructive conversation - but that doesn't preclude working with her to find a good compromise if the needs of the organisation are shifting to need that work done later in the day.

In reply to Nina Waters:

I'm glad you said that, Nina, because it occurred to me as well. If someone tells you that a health condition will cause them to be more prone to error later in the day, what kind of idiot would decide that's when they will compel the person to work?

@Clarky - don't quote me to the business!! It might be inflammatory. Sometimes in HR you can't help questioning some people's common sense, or lack of it ... ...

In reply to Elizabeth Divver:

Thank you Nina and Elizabeth. Agree with all you say. Many thanks for the advice.