Just a point or two about photography in the UK:

Anyone in a public place has no right to privacy, and you can't stop people taking pictures of you. If you're actively harassing someone, e.g., by following them round to take pictures, or sticking your camera in their face, that's different and you could be breaking the law.

If you're on private land, or in a museum, gallery or theatre, technically you must seek permission to take photos. Of course, this is very loosely observed, and in practice no-one's really going to object if you're taking photos of your kids at Hampton Court, for example. But any venue is entitled to make its own rules: if they say no photography, or no flash, etc., you must observe those restrictions. Their maximum sanction is to ask you to desist, and if you persist you can be asked to leave. No-one may seize or damage your camera, make you hand over your memory card, nor insist that you show them your photos or make you delete them.

There is no law saying that you can't take a photo of a policeman in the street. It might not be entirely sensible so to do. If an entertainment venue hasn't explicitly forbidden photography or videos, they would have an uphill struggle to stop you, though they'd be within their rights to get you to desist. I doubt whether offended individuals would be able to take it on themselves to act, other than making a polite request to desist. I suppose you could ask the venue's organisers to intervene, though they could have other things on their minds.

I don't know what the rules are in other countries. I have hundreds of photos that I've taken without challenge inside European churches and galleries, including the Uffizzi, Bargello and Accademia in Florence and the Vatican Museums and Sistine Chapel in Rome (though the latter does have signs up which just about everyone ignores - you seem to be generally OK as long as you don't use flash, and camera phones are far less prominent than huge great SLRs).

But rules are just rules. Common sense, discretion and consideration for others should be the only rules we need, on the whole.