A client was interviewd under caution back in March but has not heard back from the HSE on whether they will be taking any further action. Is there a protocal on the timescale HSE to take to get back to a client?

I echo bob, it can take years for them to bring a precaution. I would not site back a wait and discuss, with legal advice, with your client what their approach will be. Plead guilty or defend it?

It is just an interview. Albeit under caution. The next step is for the investigating authority to assess the evidence, see if there is a public interest or other circumstance which will influence the next step and then make a decision over prosecution or other action. You will have a really good idea of what will come your way but unfortunately you have no influence over how long the process will take. You should prepare for the worst and put right whatever it was that was wrong. Show that things have improved and show how your firm will enhance their safety in the future by way of mitigation. Not improving will not got down well with the authorities. Graham