This may seem strange coming from me, but I do not have a problem with people reporting suspicious behavior to the police, including people taking photos of unusual objects or in a furtive or, well, suspicious manner.
My fear is the police seem to be responding in a manner that indicates that all photography is illegal unless they give the OK, which at least in the US, is not true.
It is the illegal actions that police have been recently taking against photographers in the UK (and in the US as well) which worry me. If they respond to a report of suspicious behavior, interview a photographer, and determine he or she is not a terrorist or engaged in illegal behavior, they should leave them in peace, not demand they delete their photos, display their photos to the police, confiscate their cameras, or manhandle them - all of which has been undertaken by various police agencies in recent days.
There are terrorists, people should be vigilant, and reporting suspicious behavior to the police is not a bad thing. Once everything is proven to be safe, go away and leave the photographer alone.