Six activists attempt to climb Europe's tallest building in a protest against oil and gas drilling the Arctic

A group of activists from Greenpeace was on Thursday attempting to climb the Shard, the tapered 310m glass tower next to London Bridge station, as a protest against oil and gas drilling in the Arctic.

In an action that was perhaps inevitable at some point after the completion last year of western Europe's tallest building, visible across much of central London, the six climbers began their ascent in the early hours of the morning.

The Twitter feed for Greenpeace UK carried a photograph of the activists, all women, in their climbing gear before they began the protest, naming them as Wiola Smul (23) from Poland, Ali Garrigan (27) from the UK, Sabine Huyghe (33) from Belgium, Sandra Lamborn (29) from Sweden, Victoria Henry (32) from Canada and Liesbeth Deddens (31) from the Netherlands.

Another tweet read: "Look up London. We're attempting to scale the Shard, Europe's tallest skyscraper."

A picture with that tweet appeared to show the group using ladders to gain access to the bottom of the 72-storey office and residential block from the roof of London Bridge station. A live webcam was following their progress up the tower.

In a later statement, Greenpeace said the Shard was chosen because it was in sight of the three London bases of the energy giant Shell, which is involved in offshore drilling in the Arctic. When the climbers reached the top of the building they aimed to "hang a huge work of art that captures the beauty of the Arctic", it added.

The statement continued: "Shell is leading the oil companies' drive into the Arctic, investing billions in its Alaskan and Russian drilling programmes. A worldwide movement of millions has sprung up to stop them, but Shell is refusing to abandon its plans."

Shell released a statement that said it respected the right of Greenpeace to engage in an "exchange of views" about their operations. It said oil and gas production in the Arctic was not new.

"If responsibly developed, Arctic energy resources can help offset supply constraints and maintain energy security for consumers throughout the world," said Shell. "We work extensively with global Arctic stakeholders to research and develop standards and best practice on biodiversity, ecology, marine sound, oil spill prevention and response, safety and health."

A Metropolitan police spokesman said: "We were called at 4.20am today to a group of protesters attempting to climb up the Shard. We are in attendance and monitoring the situation along with British transport police."

A spokesman for the building, designed by the Italian architect Renzo Piano, said: "The Shard is being used by protesters as part of a campaign. Our primary focus is on the safety of the protesters and the workers and visitors to the building. We are working with the relevant authorities to try to ensure the safety of those concerned."

Henry, speaking from a mobile phone as she perched two thirds of the way up the Shard, said the expedition had gone well so far. "It has been pretty challenging and we are all exhausted because we are carrying a lot of weight and have been going since early this morning but it is going really well."

She said the group, who had been snacking on energy bars and gels, was now gathered on a ledge and preparing for the final pitch. "We keep coming across zones where we get reception and we pick up all these support texts and messages which is really keeping us going. It seems that our message about what is happening in the Arctic is really getting out there."

As she spoke she said she was now high enough above London to gain panoramic views of the capital. "It is quite quiet up here and we so high now that we can't really see any people anymore – the trains coming and going at London Bridge look like little electric worms."

And she said the group would soon be able to see the Shell buildings. "If I were an executive sitting in those offices today I would be worried because I think people are going to start asking a lot of questions about exactly what is going on in the Arctic."

Greenpeace said the climbers used a combination of traditional mountain climbing techniques, rope access techniques used by commercial building climbers and some free climbing. The building has an external metal frame providing handholds and crossbeams all the way to the top.

Each stage of the climb would require the lead climber to free-climb a section of the building. Once they reached a secure position, they would fix a rope to the external skeleton of the building and the rest of the group would follow using the rope. All the climbers were wearing harnesses, meaning they would not fall more than six metres if they slipped.

The British Mountaineering Council training officer Jon Garside said there was a "rich history of people climbing buildings both for recreation and for protests". He said the climbers appeared to have standard kit used by workers on tall buildings around the world and that what they were doing, while inherently risky, was fairly common practice. "Any Londoner will see all the time access workers abseiling down large buildings like the Shard to clean the windows," he said.

Greenpeace have a long history of disruptive, eye and headline-catching protest. The Arctic region, and particularly oil and gas exploration, has become a major focus for their activity in recent years.

In August 2012 a group of activists including international executive director Kumi Naidoo climbed on to an Gazprom drilling rig being constructed off Russia's north-east coast. Employees reportedly pelted the group with water, chains and other heavy objects.

In July of the same year Greenpeace protesters shut down 74 petrol stations across the UK by using the stations' emergency shut off switch.

At the same time, the fake Arctic Ready campaign was embarrassing Shell by mimicking their own publicity while making statements such as "Birds are like sponges … for oil". In 2011, the organisation sent more than 60 campaigners, including dozens dressed in polar bear suits, into the Edinburgh offices of Cairn Energy whose oil rig they had boarded a month before.

Futerra Sustainability Communications cofounder Solitaire Townsend said Greenpeace was a trendsetter at harnessing global attention through the use of social media and technology. But she said this action was a "ramp up" compared with past efforts.

"Campaigning used to be about how many people you got on your demo. With six people doing something Greenpeace has managed to get tens, if not hundreds of thousands of Brits involved in this campaign. This is the new paradigm. It's not about how many feet you've got on your march it's about how many tweets you've got on your hashtag," she said.

© Guardian News and Media 2013

Watch the video, uploaded to YouTube by The Telegraph.