Reuben Powell is an unlikely terrorist. A white, middle-aged, middle-class artist, he has been photographing and drawing life around London's Elephant & Castle for 25 years.

With a studio near the 1960s shopping centre at the heart of this area in south London, he is a familiar figure and is regularly seen snapping and sketching the people and buildings around his home – currently the site of Europe's largest regeneration project. But to the police officers who arrested him last week his photographing of the old HMSO print works close to the local police station posed an unacceptable security risk.

"The car skidded to a halt like something out of Starsky & Hutch and this officer jumped out very dramatically and said 'what are you doing?' I told him I was photographing the building and he said he was going to search me under the Anti-Terrorism Act," he recalled.

For Powell, this brush with the law resulted in five hours in a cell after police seized the lock-blade knife he uses to sharpen his pencils. His release only came after the intervention of the local MP, Simon Hughes, but not before he was handcuffed and his genetic material stored permanently on the DNA database.

But Powell's experience is far from uncommon. Every week photographers wielding their cameras in public find themselves on the receiving end of warnings either by police, who stop them under Section 44 of the Terrorism Act 2000, or from over-eager officials who believe that photography in a public area is somehow against the law.

Groups from journalists to trainspotters have found themselves on the receiving end of this unwanted attention, with many photographers now fearing that their job or hobby could be under threat.

So serious has the situation become that the MP and keen photographer Austin Mitchell, chairman of the Parliamentary All-Party Photography Group, tabled an early day motion last March deploring the "officious interference or unjustified suspicion" facing camera enthusiasts around public buildings, where they are increasingly told that it is against the law to photograph public servants at all – especially police officers or community support officers – or that members of the public cannot be photographed without their written permission. The Labour MP is now calling for a photography code for officers so that snappers can continue going about their rightful business.

Yet, according to the Association of Chief Police Officers, the law is straightforward. "Police officers may not prevent someone from taking a photograph in public unless they suspect criminal or terrorist intent. Their powers are strictly regulated by law and once an image has been recorded, the police have no power to delete or confiscate it without a court order. This applies equally to members of the media seeking to record images, who do not need a permit to photograph or film in public places," a spokeswoman said.

But still the harassment goes on. Philip Haigh, the business editor of Rail magazine, said the bullying of enthusiasts on railway platforms has become an unwelcome fact of life in Britain. "It is a problem that doesn't ever seem to go away. We get complaints from railway photographers all the time that they are told to stop what they are doing, mainly by railway staff but also by the police. It usually results in an apologetic letter from a rail company," he said.

In the summer, armed police swooped on a group of trainspotters known as the Steam Boys as they waited with high-powered photographic equipment to capture a 1950s engine called The Great Marquess as it crossed the Forth Bridge near Gordon Brown's constituency home in Fife.

The National Union of Journalists (NUJ) has also taken up the cause, highlighting the case last month of the photographer Jess Hurd, whose camera was taken from her when she was detained for 45 minutes under Section 44 while documenting a traveller wedding in London's Docklands. Last week police were filmed obstructing photographers covering a protest at the Greek embassy in London. Scotland Yard promised to investigate.

Jeremy Dear, the general secretary of the NUJ, said: "It's time the police realised that taking photographs doesn't automatically mean you're a terrorist. Every month the NUJ finds itself dealing with yet more cases of officers infringing journalistic freedoms and, very often, exceeding their legal powers.

"Even the police's own guidance makes it clear that there's nothing in the Terrorism Act that can be used to prohibit the taking of photos in a public place. The authorities have got to do more to ensure that those people charged with upholding the law don't keep on contravening it by trampling over well-established civil liberties."