There is probably a better way, but if you use the reassign action at the 100% point in the Response Level to reasign to the group it currently assigned to, but with a special title, then you have something to write a query against.
How do you set the title on this Dave?
Sorry Graham should have been clearer/right! Set the *notification* on the same escalation action time with the Is breach set and use a placeholder current assigned group somewhere in the subject plus other text to make it something you can spot. Send the notification to a role that you don't use for anything else. Now it's been a while since I tried this, but from memory that gives you an escalation action that you can query. The status of that action will say if it has expired and if it's the breach point, that should give the information needed.
I think Karen Peacock might have commented on a similar query a while back, so it's probably worth searching for that too
Thanks Dave and Karen
Looks good and I'll be able report on that just by filtering on title criteria