George King, 19, describes slipping near the top and wearing disguises to stake out the London skyscraper

Teenage climber George King became a viral sensation after scaling the UK’s tallest skyscraper without ropes at dawn on Monday – but he nearly did not make it.

As the 19-year-old personal trainer clambered past the Shard’s viewing platform, as London started stirring 300 metres (1,000ft) below, generators began pumping dust on to the metal bars he was climbing and he slipped.

“[The dust] made the panels slippery so there wasn’t that much traction,” he said. “My feet started to slip a bit which was quite worrying but I just kept my composure, took a few deep breaths and carried on.”

Within 45 minutes King had made it to the top of the central London skyscraper, where he was met by police officers. It was a feat he had planned since first seeing the Shard on a school trip six years ago. Reaching the top was magical, he said.

“Seeing how much our bodies and minds are really capable of doing when everything’s firing at once – the endorphins, the adrenalin, the serotonin – to optimise your survival, that feeling is truly profound,” he said.

For the last eight months, King has been meticulously preparing for the stunt, which he completed without ropes or suction cups. He moved from his parents’ home, in Oxford, to Leyton, in east London, to be closer both to the Shard and to the capital’s climbing gyms.

The teenager would check out the building’s security operations in various disguises, sometimes wearing a suit, other times in sports gear, in order to avoid being spotted and potentially handed a restraining order.

It was a practice inspired by his idol, the French highwire artist Philippe Petit, who employed crutches to more easily breeze past security ahead of his tightrope walk between New York’s Twin Towers in 1974.

King, who said he became “obsessed” with the potentially fatal and illegal challenge of climbing the Shard, also made model parts of the structure to better his understanding of how to tackle it.

“I wanted to see how far the human body and mind can go,” he said.

Play Video 0:25 Free climber scales Shard skyscraper in London – video

King’s passion for free soloing – climbing without rope or protection – began aged 13, when he got stuck climbing a 10-metre wall without a rope or a harness. “Something took a hold of me and I was able to get back down to the bottom,” said King. “Suddenly it struck me how far I was able to go.”

The teenager took up competitive boxing, ran a 62-mile ultramarathon at 16 and by the age of 17 had ditched climbing walls for scaling cranes on construction sites, with only chalk on his hands and climbing shoes for grip.

In August last year, he became the first person to free solo the world’s tallest climbing wall, which is 37 metres high, in Groningen in the Netherlands.

But for King, climbing the Shard – his first unaided climb on a highrise building – was monumental. “Half of my life has been perfecting for this,” he said. The teenager admits there are big risks involved with such an endeavour, but says while he was up there he thought of nothing but getting to the top.

“It has to all be intuition and it has to all be second nature,” he said. “When you’re in the moment, it is far more beneficial to have zero fear and zero thoughts.”

When he did reach the Shard’s summit, some time after 5.15am, King was met by police who had been alerted by an onlooker. “They didn’t arrest me, they were very calm,” he said.

King’s parents, who acknowledge his passion but do not condone the danger he puts himself into, found out the news via the radio.

“They knew I was up to something, but I don’t think they expected it to be the Shard,” said King. “But when my mum heard it on the radio she instantaneously thought ‘that must be George’.”

George King ascending the Shard. Photograph: Insta: @powers.of.passion

Among the buildings King plans to free solo in future is the 1,000-metre-tall Jeddah Tower in Saudi Arabia, although he wants to do so with a permit this time.

King said he has been inundated with less adrenaline-fuelled opportunities. By Wednesday morning he had received offers over social media from motivational speech organisers and a modelling agency.

“I’m open to any opportunity as long as it’s not ridiculous – why not,” said King. “Lots of things are popping up and I’m just taking what I can.”

Since Monday, he has already doubled his number of followers on Instagram after posting both drone and camera footage of his Shard climb. He didn’t wear a head camera because “it was too much of a distraction”.

At least for a little while, though, King said he will take his foot off the pedal and get back to being a typical 19-year-old. “In the last eight months I was so invested in this. Now it’s finally time to see people I haven’t seen for a while.”