There is little to no restrictions in taking photos or recording videos at tourist hotspots. There may be some exception to the rule, but there will be clear signs warning tourist not to take photos or record videos. If you want to pose with the locals, you must ask for permission, as people can be very private, and this can be considered offensive. Also, to take your photos you may also want to get portraits made. Many talented tourists are roaming the streets of cities like London, and they can make different portraits for you at very reasonable prices. And since the UK is a very busy tourist’s country, it can be difficult to get good and clear pictures of famous monuments, so you have professional photos taken by photographers present on-site or by the painting of the same.