Cut and paste from Wikipedia: -

"In general under the law of the United Kingdom one cannot prevent photography of private property from a public place,[citation needed] and in general the right to take photographs on private land upon which permission has been obtained is similarly unrestricted.[citation needed] However, landowners are permitted to impose any conditions they wish upon entry to a property, such as forbidding or restricting photography.[citation needed] Two public locations in the UK, Trafalgar Square and Parliament Square, have a specific provision against photography for commercial purposes without the written permission of the Mayor,[1] or the Squares' Management Team and paying a fee,[2] and permission is needed to photograph or film for commercial purposes in the Royal Parks.[3]

Persistent or aggressive photography of a single individual may come under the legal definition of harassment.[4]

It is a criminal offence (contempt) to take a photograph in any court of any person, being a judge of the court or a juror or a witness in or a party to any proceedings before the court, whether civil or criminal, or to publish such a photograph. This includes photographs taken in a court building, or the precincts of the court.[5] Taking a photograph in a court can be seen as a serious offence, leading to a prison sentence.[6][7] The prohibition on taking photographs in the precincts is vague. It was designed to prevent the undermining of the dignity of the court, through the exploitation of images in low brow 'picture papers'.[8]

Photography of certain subject matter is restricted in the United Kingdom. In particular, the Protection of Children Act 1978 restricts making or possessing pornography of under-18s, or what looks like pornography of under-18s. However, the taking of photographs of children in public spaces is not illegal.

It is an offence under the Counter-Terrorism Act 2008 to publish or communicate a photograph of a constable (not including PCSOs), a member of the armed forces, or a member of the security services, which is of a kind likely to be useful to a person committing or preparing an act of terrorism. There is a defence of acting with a reasonable excuse, however the onus of proof is on the defence, under section 58A of the Terrorism Act 2000. A PCSO cited Section 44 of the Terrorism Act 2000 to prevent a member of the public photographing him. Section 44 actually concerns stop and search powers.[9] However, in January 2010 the stop-and-search powers granted under Section 44 were ruled illegal by the European Court of Human Rights.

Following a prolonged campaign, including a series of demonstrations by photographers dealt with by Police Officers and PCSOs, the Metropolitan Police was forced to issue updated legal advice which now confirms that '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' and that 'The power to stop and search someone under Section 44 of the Terrorism Act 2000 no longer exists.'[10]

It is also an offence under section 58 of the Terrorism Act 2000 to take a photograph of a kind likely to be useful to a person committing or preparing an act of terrorism, or possessing such a photograph. There is an identical defence of reasonable excuse. This offence (and possibly, but not necessarily the s.58A offence) covers only a photograph as described in s.2(3)(b) of the Terrorism Act 2006. As such, it must be of a kind likely to provide practical assistance to a person committing or preparing an act of terrorism. Whether the photograph in question is such is a matter for a jury, which is not required to look at the surrounding circumstances. The photograph must contain information of such a nature as to raise a reasonable suspicion that it was intended to be used to assist in the preparation or commission of an act of terrorism. It must call for an explanation. A photograph which is innocuous on its face will not fall foul of the provision if the prosecution adduces evidence that it was intended to be used for the purpose of committing or preparing a terrorist act. The defence may prove a reasonable excuse simply by showing that the photograph is possessed for a purpose other than to assist in the commission or preparation of an act of terrorism, even if the purpose of possession is otherwise unlawful.[11]"