This card is a signpost to a DNR order rather than a DNR order in itself. As a volunteer ambulance attendant, I have to be very clear what my patients' wishes are before transporting them particularly in the case of the terminally ill, or any other individual who has a higher than normal chance of needing to be resuscitated during transport.

Without a formally signed DNR order drawn up by a solicitor, professional and volunteer ambulance crews are duty-bound to attempt resuscitation.

Tom Reynolds mentioned the difficult decision over whether to resuscitate here: http://randomreality.blogware.com/blog/_archives/2005/1/25/279867.html

Been there before. Many areas in London which appear to be public are in fact private land, the South Bank for example.
In many areas "professional photography" is often verboten, and tripods aren't welcome. This being the UK, a tripod ban is for health and safety reasons, obviously. Pro photography being banned in places like Tate Modern's turbine hall or St Paul's cathedral is understandable for locations that derive income from selling their image.

I had a run-in with a jobsworth security guard a while ago. Unfortunately for me, he told me professional photography wasn't allowed. I'm not a professional, and so a battle of wits ensued