The ACAS guidelines say

46. Where an employee raises a grievance during a disciplinary process the disciplinary process may be temporarily suspended in order to deal with the grievance. Where the grievance and disciplinary cases are related it may be appropriate to deal with both issues concurrently.

So there is some leeway. However I would want to know why a grievance raised "a long time ago" hasn't been resolved yet (if resolution is only that there is no case to answer etc). I would be concerned that you have failed to deal with the grievance and if there was substance to it then how that would affect their absence and therefore the current disciplinary process.

Why cant the grievance process be concluded?

But all told it seems an incredible amount of time to handle both the disciplinary and the grievance and that also causes me concern

In reply to Keith:

It has been incredibly complicated process which I can't really go into on here.
But are we allowed to continue with our sickness management process?

In reply to Jenny:

What stage has the grievance reached and why hasn't it been concluded? How relevant is the grievance to the disciplinary?

In reply to Keith:

We have had a lot of resistance in meeting attendance and the goal posts seem to keep changing.

There was no disciplinary, it was just an investigation which we were unable to undertake due to the sick absence beginning the next day.

My question is relating to absence management. I understand it’s a catch 22 due to the need to do the grievance to move forward and hopefully alleviate the stresses, however we have not been able to hold more than an informal grievance discussion. But we still need to go through our sickness absence procedures.

In reply to Jenny:

Sorry I still don’t understand why management can’t hear the grievance. It’s what we are paid to do. Yes it can be difficult. But cutting through that and managing the process to conclusion should be your number one goal.

If for example the grievance is around bullying, unfair workload and victimisation by their manager. Then not concluding before you go down a process to dismiss for absence that arguably has been caused by the actions they accuse you of would almost certainly be unfair.

Cut through the noise. Get to heart of grievance and sort it one way or other would be my advice before you dismiss in the alternate process.

It does rather sound like you've made a rod for your own back, here. As a point of fact, I should say that there's no such thing as an "informal investigation". There's either an investigation or there isn't, and the point of the investigation is to establish whether there is a need for further action which might be informal or formal.

I don't understand why this investigation stopped. The subject of the investigation was sick but, presumably, other witnesses and contributors could still be interviewed? I have conducted interviews with people who are absent by phone and even in their own homes when it was appropriate and, with COVID, we've all become au fait with video conferencing. Being stressed doesn't stop someone being able to be interviewed (or the Police would never get anything done). If a person refuses to participate then you just use the evidence available to reach a recommendation.

I also don't understand why you can only communicate via the union representative. This is grossly exceeding the duties of the union rep in this kind of case. They are there to support the employee, not speak on their behalf. If the union rep can communicate with your sick employee there's no reason you can't communicate with them yourself.

I'm afraid it sounds like you're letting the employee and their rep run rings around you, with every conceivable delaying tactic. I fear you're right that this will end up at an ET and the tribunal panel will be asking you some very hard questions about your policies and processes.

Thankfully, though, all may not be lost. I would advise you to re-engage with the employee with a letter setting out everything that has happened so far and clearly stating where you believe matters lie. Keep the rep in the loop, but stop communicating through them. You need to press on with the absence management process, complete the original investigation (it might be that, after all this time, the correct outcome is "no further action") and deal with the grievance. Unless the grievance is directly related to the absence issue, there is no reason to stop one to deal with the other, as Keith has pointed out.

If the employee is able to attend meetings to deal with the grievance, they should equally be able to attend meetings to deal with their absence and you can roll the two together.

However, you need to be prepared for the possibility that this employee will simply return to work and you need to decide now whether that is an outcome you are prepared to accept. If so, all well and good - proceed as described. If not, though, you should make preparations for a Settlement Agreement as, with the abortive disciplinary investigation far too stale to proceed, there may be no other way to exit this employee if she ends her sickness absence.

I would encourage you to reconnect with the representative with a letter setting out all that has happened up until now and plainly expressing where you accept matters lie. Keep the rep on the up and up, yet quit conveying through them.