Its all well and good saying "leave it to the council". The problem comes however when the mess hits the fan,the building is on fire, and crews are pulling out barbequed squatters in the wee small hours of the night.
Cue some very twitchy senior fire officers asking if anyone in their organisation knew about the premises, and if so what they did to try and have it secured. You might also get the local press making similar enquiries too.
So as long as you can say you did all you could then great. Could you issue an enforcement notice? I reckon it might be worth a try, especially if the council fail to act, because despite it being their responsibility some are stating they just don't have the cash now to secure sites like this - there is only a limited budget set aside for securing buildings and those budgets soon get used up very quickly at the moment (sign of the times).
If the site is targetted by arsonists (rife at the moment), and the fire spreads to neighbouring buildings, and businesses what are the possible social/economic conseqences, let alone risk to life and limb? What about things like lost trade, loss or disruption to community resources, the drain on emergency service resources dealing with the blaze?
Somehow Im not sure it is a case of just leaving it to the council. My advice is if they don't play ball then don't just leave it there. Can one of your senior officers talk to one senior at the council? Can someone speak to the owners of the void premises?. If they don't bare any fruit maybe see if your legal team will go with the issue of an enforcement notice. Its got to be worth a punt in my view.