Media and civil liberties groups have expressed alarm after the managers of an Olympic venue pledged to intercept and question anyone seen photographing or filming the site, even from public land, and defended security guards who wrongly tried to invoke terrorist laws to prevent footage being shot of the arena.

The stance taken by the O2 in Greenwich, south-east London, which will host this summer's basketball, wheelchair basketball, artistic gymnastic and trampoline events, highlights wider concerns that Olympic security operations could see photographers, film crews and even members of the public harassed for entirely legal activities.

John Toner from the National Union of Journalists said he would seek an urgent meeting with managers of the O2, saying their tactics had no basis in law. "I'm stunned, and what they say is utterly outrageous," he said.

While there are strict photography rules inside Olympic venues and on many other private spaces, when standing on public land the press and public have a clear right to shoot still or moving images.

Ahead of the Games, police and the security industry have sought to train staff about this aspect of the law. There have nonetheless been a series of incidents in recent months in which photographers have been challenged while working on public land, especially in London.

As an experiment, the Guardian attempted to shoot video footage of the O2 arena from a public road on its southern edge, only a few minutes' walk from the main entrance.

Very quickly the reporter was challenged by O2 security guards, who made a series of demands with no basis in law. They ordered that the filming stop – "We've requested you to not do it because we don't like it" – and that they be shown any existing footage. Asked on what basis they could demand this, one replied: "It's under the terrorist law. We are an Olympic venue." Another added: "You have, for want of a better word, breached our security by videoing it [the O2]."

At one point they refused to allow the reporter to leave. One said: "It's gone too far for that."

Guards are entitled to challenge suspicious behaviour and call the police. However, they have no additional legal powers on public land. While such overreach is not uncommon it is often followed by a management apology.

An O2 spokesman defended the guards' approach. He said: "On the basis that [the reporter was] filming areas of the O2 that are not usually of interest to the public, our security staff's approach and handling of the situation was entirely appropriate."

It was routine policy to intercept anyone filming the arena from public land, he added: "We work with the media and others to accommodate requests to film in and around the O2, which is situated on private property, but when we observe filming of the O2's infrastructure and access points it is our policy to approach individuals so we can take the appropriate course of action." The same policy was in force with people taking still photographs from public vantage points, he said.

The civil rights campaign group Liberty said it was alarmed. Its legal officer Corinna Ferguson, said: "There's no power stopping a person taking photographs on public land, let alone to arrest them or seize property, without reasonable suspicion they've committed an offence. Police officers or security guards who get this wrong could well find themselves in trouble with the law.

"With all eyes on London during the Olympics what a terrible message it would send if Londoners and tourists face harassment from the authorities merely for snapping the capital's landmarks."

Toner, who set up a meeting last week between journalists and senior Scotland Yard officers leading the Olympic security operation, in part to address such concerns, said: "The level of ignorance displayed by their employees is quite incredible. But for the management to display the same level of ignorance is beyond belief.

"What worries me is that there must be lots of people who will just come along and take pictures of the O2. It's an unusual building. Some will be tourists – are they going to clamp down on tourists? Are they going to alienate visitors with their ridiculous behaviour?"

The O2's policy is all the more surprising given recent guidance issued by the British Security Industry Association. It has drawn up a leaflet for members which spells out the law very plainly. "If an individual is in a public place photographing or filming a private building, security guards have no right to prevent the individual from taking photographs," it reads, adding that filming or taking a photograph "does not in itself indicate hostile reconnaissance or other suspicious behaviour".

Similar incidents with police were relatively common until 2010, when terrorism stop-and-search laws were tightened following a challenge at the European court of human rights. Since then, according to experts, it has mainly been private guards causing such problems.

"Our main worry is the lack of training for some security guards. It seems to be one of the big issues now," said Chris Cheeseman from Amateur Photographer magazine, which has campaigned over photographers' freedoms.

The incident at the O2 was eventually resolved after guards called police, who also asked to see the video footage, citing the Terrorism Act. The reporter was allowed to leave after neither he nor the police could properly operate the camera to replay the footage.

The photographer's experience

As a photographer in the heightened security atmosphere of pre-Olympics east London, Vickie Flores is used to being challenged. But this seemed particularly anomalous: being told she couldn't take pictures of a 60m-high structure clearly visible for miles around.

"Not a week goes by without me being stopped by someone or other. But this one was bizarre," Flores said of her recent encounter with a security guard near the almost-completed Thames cable car system, which will whisk tourists between Olympic venues on opposite sides of the river using gondolas suspended between soaring white pillars.

Flores ignored the direction – she was taking the picture from a public pavement. But she has found such attitudes hardening as the Olympics approach, especially among over-officious security guards.

"I've never been stopped as much as I have in the past six months," she said. "It's happened more than in the rest of my life before. Sometimes I even think, 'Can I be bothered with all the hassle of taking a particular picture, is it worth it?' It's got to that stage."