The debate on whether you can take photographs (especially with a tripod) on private or public land and encountering overzealous security guards seems to be an issue that will never go away and sadly it seems that we are moving more and more towards an undemocratic model of land ownership.
The issue should be simple: if it’s private land, then you need to get permission from the landowner but there is nothing to stop you from taking photographs of private buildings from public land/right of way. No doubt, an ill-informed security guard will try to move you on from taking a photograph of ‘their’ building but they are not within their rights to do so. However, if you wander onto private land, then you can be done for trespass.
If you are asked to move on from public land, then ask to see a copy of their regulations and even ask the security guard to call the police – the police are well informed about the rights of photographers and this was demonstrated in an experiment in 2011 called ‘Stand Your Ground’ : http://youtu.be/FJH9F7Hcluo
Some privately owned land in London includes: Kew Gardens, Paternoster Square, Canary Wharf, the London Underground , the land between Land Bridge and Tower Bridge and surprisingly, the South Bank. You are more likely to run into trouble if they think that the photographs are being used for commercial purposes, so if you are stopped then be polite (yes, it’s hard if you are confronted by a hostile guard) and just move on because getting involved in a pointless argument with a jobs worth is not worth it. If you’ve got your image, then great, it’s yours and they cannot insist that you delete them.
What about photographing people in the street? There is no right of privacy in UK stating that you cannot take pictures of people in public places but you can run into trouble if you publish the images (especially if the person is identifiable). If you take a photograph of someone in the street and they object, then the courteous approach is to explain that you are a photographer, apologise and offer to delete the image. And definitely do not take images of other people’s children without their permission – this is likely to land you in a lot of trouble (i.e. being arrested) and having all your images deleted.