The latter is at risk - do you know they have one on file? What if it wasn't submitted for approval by the prior owner?,
the indemnity insures against anyone at any time in the future ringing them up and asking questions that could result in the structure being deemed unsafe or not permitted, or they turn up out of the blue or are on site for another matter entirely (like attic conversion) - covering costs to rectify or replace.
If you go poking around now (with not much knowledge on the history of it), I fear you won't then be able to go back to door number one and get cover, it could be at your full cost (or de-value).... like taking car insurance out after the car crash
*please check exactly with your solicitor but it's was I recall from a few yrs back now