Why should a tourist taking a picture of the BT tower or a London square (like Connaught Square) be required to account for his actions? It seems that the job of the police and security forces is to protect the interests of the rich and the powerful. I was `happrehended` after taking a pic of Tony Blair's £3.5 million abode in 29 Connaught Square:
 https://www.indymedia.org.uk/en/regions/world/2009/07/434061.html?c=on#c227874

I was asked to delete a photo - laughably, the one they asked me to delete was one of the garden of my hotel which was some 2 miles from Connaught Square. When I pointed out this gaffe the WPC changed the subject and happily I was not sent to the tower.

Seriously, though, isn't asking someone to delete a photograph like destroying evidence (evidence of what? in my case) or something like that?

Paul.

They can't make you, nor can they do it themselves:

"Members of the public and the media do not need a permit to film or photograph in public places and police have no power to stop them filming or photographing incidents or police personnel. "

"Officers have the power to view digital images contained in mobile telephones or cameras carried by a person searched under S44 of the Terrorism Act 2000, provided that the viewing is to determine whether the images contained in the camera or mobile telephone are of a kind, which could be used in connection with terrorism. Officers also have the power to seize and retain any article found during the search which the officer reasonably suspects is intended to be used in connection with terrorism."
Photography and Section 44 of the Terrorism Act 2000

"Officers have the power to view digital images contained in mobile telephones or cameras carried by a person searched under S43 of the Terrorism Act 2000 to discover whether they have in their possession anything which may constitute evidence that they are involved in terrorism. Officers also have the power to seize and retain any article found during the search which the officer reasonably suspects may constitute evidence that the person is involved in terrorism."
Photography and Section 43 of the Terrorism Act 2000

"Any officer making an arrest for an offence under Section 58a must be able to demonstrate a reasonable suspicion that the information was of a kind likely to be useful to a person committing or preparing an act of terrorism.

It should ordinarily be considered inappropriate to use Section 58a to arrest people photographing police officers in the course of normal policing activities, including protests, as without more, there is no link to terrorism.

There is however nothing preventing officers asking questions of an individual who appears to be taking photographs of someone who is or has been a member of Her Majesty’s Forces (HMF), Intelligence Services or a constable. "
Section 58a of the Terrorism Act 2000

Straight from the trotters hoof:
 http://www.met.police.uk/about/photography.htm

This is worth a look at - more on the Mets "advice" on photography in a public places from Marc Vallee in The Guardian.
 http://www.guardian.co.uk/commentisfree/libertycentral/2009/jul/09/photography-anti-terrorism-regulations