One of the country's leading architectural photographers was apprehended by City of London police under terrorism laws today while photographing the 300-year old spire of Sir Christopher Wren's Christ Church for a personal project.

Grant Smith, who has 25 years experience documenting buildings by Richard Rogers and Norman Foster, was stopped by a squad of seven officers who pulled up in three cars and a riot van and searched his belongings under section 44 of the Terrorism Act, which allows police to stop and search anyone without need for suspicion in a designated area.

"Three of them descended on me and said they were here because of reports of an aggressive male," Smith said. "One of them even admired my badge which said 'I am a photographer not a terrorist'. But they searched my bag for terrorist-related paraphernalia and demanded to know who I was and what I was doing. I refused. saying that I didn't have to tell them, but they said if I didn't they would take me off and physically search me."

Smith's trouble began when he refused to provide his name and explain what he was doing to a security guard from a nearby Bank of America office. He said he was astonished by the police response, not least the expense of dispatching four vehicles and seven officers.

His experience comes despite a warning last week to all police forces not to use section 44 measures unnecessarily against photographers. In a circular to fellow chief constables, Andy Trotter, of British Transport police, said: "Officers and community support officers are reminded that we should not be stopping and searching people for taking photos. Unnecessarily restricting photography, whether from the casual tourist or professional, is unacceptable."

In the past 18 months there have been 94 complaints to the Independent Police Complaints Commission about the misuse of section 44 powers. There is a growing outcry among working photographers who are finding their daily routines interrupted by police searches when working in high-profile areas that may be considered terrorist targets.

City of London police said its response to Smith had been proportionate. "When questioned by officers, the man declined to give an explanation and he was therefore informed that in light of the concerns of security staff and in the absence of an explanation, he would be searched under the Terrorism Act," said a spokesman. "After the man's bag was searched, he explained he was a freelance photographer taking photos of buildings. Once this explanation was received there was no further action."