I understand the Police will have their reasons for not disclosing any details but i feel the response from MPS Forest Hill is downplaying the incident somewhat.
That many Police cars, vans, unmarked cars, ambulances, sniffer dogs and the sheer amount of officers in varying roles would indicate this was a relatively serious incident (or at least they had reason to believe it was).
I heard them use the word negotiator and other people have mentioned it was potentially a hostage situation. People, including myself, are curious when this amount of activity happens directly outside your home. Perhaps it would help further presumptions if the authorities released a short statement?