It's tough at the top: Meet the builders behind Europe's tallest tower

The cramped crane cabin that Andy Bowden spends 12 hours working inside every day is much the same as any other. There is his leather swivel seat armed with two small levers to control the hoist, a heater to keep both him and his flasks of soup warm, and a roll of loo roll that he insists is purely for his runny nose.

What makes his job and his otherwise ordinary cab unique is the crane's location – peaking out of the concrete summit of what will be Britain's tallest building, the Shard in Southwark, south London – and the magisterial view out of its window. The sun has just gone down at the start of a beautifully clear winter's evening in London, and the capital's streets 259 metres below are beginning to glow orange like rivers of copper flowing through channels of black stone and steel. No wonder that just beneath the crane, one man is standing on tiptoe on a crate with his hands aloft so his camera can get a glimpse of the spectacular vista obscured by the safety boards.

Looking out at this panorama every day, Bowden seems to have more in common with the pilots flying above him than with the City workers down below. "The other day, we were above the cloud and you couldn't see anything apart from the tip of Canary Wharf," he says. "It's nice, you get away from it all. You're not with all the noise and clattering and banging. You're on your own." The Shard's crane co-ordinator, Adam Blakeley, is similarly reflective, saying wistfully: "It's surreal. You get personal experiences when you're up a crane."

When the Shard is completed in mid-2012, it will stand 310m tall, the equivalent of 87 storeys, with a public viewing platform on the 72nd floor. Until then, the cityscape is the preserve of Bowden and his fellow construction workers. But for all the wonder of the sights they are treated to, working on a building site a quarter of a kilometre up in the air is highly risky. Just to get to work in the morning, crane workers get up to the 72nd floor via first one lift that goes a third of the way up the interior of the building, and then another external elevator that runs up the side of the building. Once there, they have to climb two ladders to get to the base of the crane, then another to get up to the small gantry at cabin level.

And a skyscraper building spree that is revolutionising London's skyline means that more and more construction workers are being asked to take on equally formidable jobs at extraordinary heights.

Already sprouting up just across the Thames from the Shard is the "Pinnacle", which will eventually reach 288m. Just down the road from that is the 230m Heron Tower, which opens next month, and within the next few years they will be followed by the 235m "Cheese Grater" and the 160m "Walkie-Talkie". Each of these is a project involving hundreds of workers performing all kinds of different roles from steel-erecting to window-cladding.

Of these, crane-operating is one of the most demanding, and potentially the most dangerous. Three men died in 2000 when a 400ft tower crane collapsed in London's Docklands while working on the HSBC Tower; despite an exhaustive investigation by the Health and Safety Executive, no conclusive explanation was found. Just three years ago, nine people were killed in New York when two crane accidents occurred within a couple of months of each other.

The operation at the Shard, which relies greatly on its six tower cranes run by a team of 18 drivers, therefore requires meticulous planning and constant risk-assessment – especially as the cranes are manned 24 hours a day and work in all kinds of weather conditions.

The main hindrance to the crane team and construction manager Steve Downton is high wind, which can cause havoc for machines sometimes lifting hauls of 18 tons and is the only type of weather – apart from lightning – to bring work to a halt. "We can live with the rain," says Downton. "Wind is our biggest enemy." Every day brings a new set of wind forecasts for various heights up to 200m, and forthcoming lifts are planned around these. The five cranes standing alongside the structure can work in winds of up to 36mph, while Bowden's crane atop the Shard's concrete core, known as TC1, must stop if the speed is more than 25mph. That can mean up to half the potential operating time is lost at this time of year, a big problem for subcontractors working to tightly negotiated timetables and deadlines.

Britain's recent onslaught of winter weather has been a particularly severe blow, according to Downton. "What we would like is cool weather with no wind, but what we're actually getting is windy weather and freezing conditions," he says. "That is the worst situation for us, because we can't pour concrete in freezing conditions and we can't lift anything in high winds, so when you've got a combination of those two, the job comes to a standstill."

Much of the time, the crane drivers are unable to see their hoists; indeed, in mist and low light they are lucky if they can see the ground at all. Constant radio communication between the crane operator and the banksman, whose job it is to put the chains around the elements that need to be lifted and to direct the operator, is therefore essential.

Inside the crane cab, Bowden and his fellow crane drivers are grateful for their heaters – the air temperature is typically several degrees lower at the top of the Shard, and reached minus 7C one day in December. But steelworkers such as foreman erector Matt Collier, fully exposed to whatever the elements throw at him, must make do simply by donning plenty of layers. Not that the summer is necessarily much more pleasant. "Handling a red-hot piece of steel isn't any fun either," Collier says. "We've had the lot: the wind, the rain, the sun. But you just get on with it."

The steel erectors have to install the large pre-fabricated columns and beams that form the Shard's bodily skeleton around its concrete spine. This holds its own degree of risk, though things have of course changed since the Empire State Building was constructed, when labourers would sit freely on girders over a quarter of a kilometre above New York City to eat their packed lunches. Collier says that the safety culture has transformed massively even since he entered the trade in 1990.

"You could do anything you wanted, within reason," he remembers. "We didn't even wear helmets then. Steel-toecapped boots weren't compulsory; we used to wear trainers on site. Everything has changed, safety-wise. But a lot of the time, people look back and wish it could be like that again. All the safety regulations do is move the risk along."

Nevertheless, some of his experiences on other building sites in the past have made him wary of the very real dangers still present in some corners of the business. "I did a job just recently where we had an 800-ton crane that was loading 50-ton beams, and it started making funny noises and creaking. I said to the crane driver, 'Is that all right?' He said, 'Yeah, no problem.' Five weeks later, it was in the yard and the back ballast fell off on the cab. If that had happened at the wrong time, we'd have had a crane in a hole and a few of the lads dead."

Accidents such as that can prove deadly even at low level. But Robert Crawford, who leads the group of cladders fitting the Shard's 11,000 windows and glass panels, says it is the sheer scale of the operation in London Bridge – rather than specifically the height of the building – that means additional care is required. "You have to be aware of the people below you, and the people above you, and everything around you," the New Zealander says in a very serious tone.

Thankfully for them, the cladders install the windows from within the building rather than outside it. Nevertheless, working hundreds of metres up on precipices open to sudden gusts of wind, they must wear harnesses strapping them to the structure itself to ensure it is impossible for anyone to fall off. Crawford adds that the men also have to be careful of any loose equipment. "At that level, even a bolt can cause damage if it gets kicked and goes flying off."

Located next to one of London's busiest train stations, the Shard is very much in the full glare of public scrutiny, making any loose bolts even more important than usual. While most building sites are out of the view of passers-by behind tall fences, no barriers could ever be high enough to obscure much of this edifice. But while there are additional risks involved in that, it also allows for one of the great charms of a skyscraper – its whole home city can enjoy watching it grow.

When the Shard is completed, it will be a beacon of modern British architecture in our Olympic year. In the meantime, however, the next time you look up to see how the work is going, spare a thought for the bloke sitting alone at the top of that crane.