Sadly, from time to time, it’s worth reminding everyone, photographers (professional and hobbyist alike), the public and even law enforcement and their uniformed civilian security colleagues, the specifics of the law. Essentially, you’re fine to shoot from public land, police and especially security guards can’t make you delete any photos, there’s no specific privacy law beyond harassment, and be aware of specific bylaws regarding private areas including Royal Parks, transport hubs etc.
The Metropolitan Police has a page with some advice, but glosses over the fact that there is essentially no difference in law between someone with a UK Press Card and someone without one, it just might get you a little more respect. More usefully, Linda Macpherson has created a PDF document that can be printed out and kept in a camera bag, should it be required. You can download it here.
