Limiting actions to current assignee or something similar

Hi,

I've recently created a simple new Change process that consists of a series of stages.

As each stage is completed, the analyst clicks on, say,  "Step1 Completed", and the Change then automatically assigns to the next analyst ready for the next stage.

This works really well, but after analysts complete their own stage, the Change stays visible on their screens with the new "Step 2 Completed" Action ready for the new assignee to click on once they've done their bit.

We are having to train our staff not to click on this.

Is there any way we can assign rights to perform actions only to the current assignee/group?

Or does anyone have any clever ways around this?

I've probably not explained this very well!  Here's the relevant part of the process.

Any help gratefully accepted - Cheers - Adam.