I don't want to go into details at this point in time but in my local town I was followed by a private security guard or Town Ranger as they are called this luchtime as I took photographs from a public place of buildings that are not sensitive in nature.
I have not encountered this before but when looking into it have found that it is increasingly becomming a problem for street photographers.
It is perfectly legal to photograph buildings and indeed people in a public place. In fact even if you stray onto private land, which I did not, you can only be asked to leave and your photographs do not have to be deleted.
Anyone else come accross this problem? The buildings I was photographing are Victorian and of historical interest but I object to being stalked while I go about my lawful business in a public place.
This website covers the relevant rights of photographers.
http://www.sirimo.co.uk/media/UKPhotographersRights.pdf