A former student who says he scaled Europe's tallest building tells Channel 4 News that the stunt was to challenge the boundaries between public and private space.

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Bradley Garrett claims his group of urban "explorers" has climbed the 310m Shard in London on three occasions.

On one occassion they snuck past a security guard and climbed 76 storeys of internal stairways making it to the red helicopter warning light.

Mr Garrett comments come after pictures apparently showing a group of trespassers posing at the top of the unfinished skyscraper were posted on his blog Place Hacking.

I feel there are a lot of places in this city that we don't have access to... and that frustrates me. Bradley Garrett, urban explorer.

The series of night-time images are said to be taken at the summit of the building.

Mr Garrett said there were other reasons for climbing the Shard: "It's the highest building in Europe, it's a spectacular view, it's quite an adrenalin rush."

But he insisted that he was also concerned about the "fuzzy" boundary between public and private space. "It's often unclear which spaces you can and can't access ... the only way really to probe those boundaries is to try it. Unfortunately most people don't"

Urban exploration

"I feel there are a lot of places in this city that we don't have access to, that we are told we can't go and that frustrates me. I enjoy that process of uncovering those hidden places and seeing what I can access. It's also for the simple fact that we get to see something that most people don't get to see."

The 31-year-old, from Los Angeles in the US, who completed a PhD on urban exploration in February, has said that he and his group had "done with" the Shard for now.

But he insists that his group would not target private, residential buildings. He said they climbed the Shard because it was a corporate building built partly with public money.

"We do not break anything, we do not alter anything, 90 per cent of the time no-one even knows we have been in and out of the place," he said.

Mr Garrett, who lives in Clapham, south-west London, said his group had first scaled the building to watch New Year's Eve fireworks over London in December 2010.

A spokesman for Sellar Property Group the developer and Mace the main contractor declined to comment on Mr Garrett's claims that it was still possible to scale the building or his claims that the group had climbed up the building "half a dozen" times.

"We believe this is an incident which took place around December 2010 when we were undertaking both ground and structure works," he said.

"The breach was discovered very soon afterwards and security immediately tightened.

"Today security on the site is tight with 14 night-time security guards on duty continuously who cover all areas, as well as 25 CCTV cameras in operation together with a ground floor level laser alarm system."

Scotland Yard said it had not received any complaints about the alleged break-in.

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