I personally don't like to have my picture taken, no particular reason except I just don't. However if I am out in public and it happens, so what, in a country (an overcrowded one) , in a public space there is nothing I can do legally to stop them. The main problem seems to lie with areas where a lot of children congregate, outside schools etc' Stand outside one, on your own with a camera of any kind and if one of the parents sees you, it is a risk I would not take for fear of being lynched! This is fully understandable considering the risk Pedophiles pose towards children. I would not do it either because I am not that way inclined.
Don't even mention security cameras. The UK is the most heavily surveyed country in the world. There are more security cameras here than anywhere else per head of population. Go about your normal business - I have no problem with that at all. Step out of line doing something illegal, then the gloves are off that person is fair game.
The way things are at present are tempered with a new regulation involving Data Protection (General Data Protection Regulations 2017) where someone can be identified from a picture that later becomes news or appears on television, the face has to be pixelated out unless express permission is granted to use it. Otherwise it is more or less a free for all with a few exceptions. On Railway Stations which are private property, Outside Military or other secure establishments covered by the Official Secrets Act. Shopping malls, again private property, The private security used by some establishments, even Government buildings, have no jurisdiction outside the doors of the premises they are contracted to protect, but there was a spell of them exceeding their authority of the grounds of 'security'. This was prevalent after the bombings on the London Underground and other places but this 'excessive vigilance' has now largely stopped.
No one, including Police have the right to demand that you delete images from a memory card, or seize film from a camera. but it is wise to let them (The police only. Anyone else tell them to take a walk) see what you have photographed, although you can refuse access to police officer, this may however make them think you have something to hide and give them cause to dig deeper. So if there is nothing of any consequence, let them look, that will be the end of the situation. If they do look further and find that you have committed an offence you could be arrested and you equipment siezed for examination, so it is best to go along with them. At the end of the day if all's well you will get an apology and your equipment back.
In UK there is a national organisation called the National Trust who look after, maintain and restore old buildings of significant historical interest. They used to refuse any permission to photograph INSIDE because of a risk of flash damaging fine fabrics etc. Not physical damage, but the light causing the colours to fade. It was only when it was pointed out that a flash only lasts around 1/5000 of a second, give or take, that they eventually relented. (Actually I think it was more to do with loss of sales of photographs they were selling in the gift shops!).
At the end of it, if a situation look a bit dodgy then hide you camera and walk away.