A working life: The Tower Bridge operator

A crowd of about 200 people is staring intently at me, cameras poised. My heart is pounding. Charles Lotter, a great bear of a man, presses the loudhailer switch and I start to speak: "Staff announcement. The bridge control system is about to be switched on. Please stand clear of all moving machinery, structures and controls."

I am about to raise Tower Bridge and although I know Lotter, a senior technical officer employed by the City of London Corporation at the bridge, has already carried out myriad pre-lift safety checks, I am still as jittery as a cat in a sack.

I press the first button of several in a row and say: "Stand by, bridge crew. About to stop road traffic."

Ahead of us, the traffic lights on Tower Bridge turn to red. Gates come down in front of peeved-looking motorists while four guards put up chains to stop pedestrians walking on to the bridge.

Once the bridge is clear of free-ranging buses and tourists, I push a button to release the immense bolts that hold the two bascules – the moving parts of the bridge – in place. I then push a lever forwards and the bascules gradually rear up in front of the control room. A computer screen shows the degree of angle and Lotter tells me to aim for 45 degrees because the sailing barge Gladys, which has requested passage, is quite small (a huge cruise liner is moored on the other side of the bridge that required the bascules to be fully raised the previous night). I overshoot slightly on the angle, but he says kindly that it doesn't matter.

Gladys glides past regally and soon I'm going through the procedure for lowering the bridge again. The whole process takes about seven minutes, much faster than I had realised. No wonder that, in 20 years of living and working in London, I have only seen the bridge raised once before, even though it opens on average about 13 times a day during peak tourist season (some tourist boats have cheekily attached faux masts so the bridge has to open for the benefit of their passengers), or 1,000 times a year.

Lotter looks just like the type of man you'd expect to be responsible for lifting bridges: tall and broad, totally calm and carrying a considerable air of authority. He is one of three senior technical officers (STO) working at Tower Bridge and although his job is primarily about maintaining the operating machinery and managing the bridge staff, he is also one of five official "bridge drivers", with a sixth undergoing training. This involves controlling the 1,200-tonne bascules, French for "see-saw" or "scales", and a name that reflects the way the huge 450-tonne counter weights pull the bridge up to let vessels taller than 30 feet (9m) through to the next section of the Thames.

So how do you learn to "drive" the bridge? "The only thing that will prepare you is doing it," Lotter says. "It's like riding a bike."

I think about how nervous I was while making the announcements and operating the bridge mechanisms, and ask him what went through his mind the first time he raised the bascules. "I felt just like you – very nervous. But it's my job and you get used to it."

Lotter, a South African by birth, trained as an engineer in his homeland doing an apprenticeship in a steel foundry and then moving into the automobile manufacturing industry, working for a plant that hydraulically pressed out car parts. He moved to the UK 22 years ago, and was working for Reuters in Docklands when he saw the job advertised at Tower Bridge. "I was one of 120 applicants," he recalls. "They were looking for someone with electrical as well as hydraulic experience, and I met both criteria."

He has worked at the bridge for 15 years this month and says: "It's the best job I've ever had. Every day is a challenge. It's never boring."

It is easy to believe that. In 1894 it was set down in law that Tower Bridge should be raised free of charge to allow passage to vessels and, provided they give 24 hours' written notice, that rule still applies.

Some drivers find it hard to accept that river traffic takes precedence. The staff at Tower Bridge are very successful at stopping people taking lemming-like leaps from one bascule to the other as the bridge opens, though some have tried. In 1958 the driver of a number 78 bus found himself caught near the edge of the south bascule as it started to rise and decided to accelerate over the gap rather than back up. No one was seriously injured.

And in May 1997, Bill Clinton's motorcade became separated from Tony Blair's when the bridge opened – again for the Gladys. The two leaders had been for lunch in the nearby Pont de la Tour restaurant, but while Blair's car just made it over, Clinton's was caught by the lights. The bridge staff recount that the second the bridge started lifting, they got a call from Scotland Yard demanding that it be closed again to let Clinton catch up with his buddy. Short of defying the laws of physics this was impossible, and the guards and their president had to wait with guns bristling until the barge had passed through in her own good time.

It's even less boring when something goes wrong with the machinery: if the bridge gets stuck while open, traffic can grind to a halt in the City and a good part of south London. The last time this happened was June when the bridge suffered a power failure: not only were the bascules wedged open, but clients at an event in the walkways above the bridge were left groping around in complete darkness.

The machinery is constantly checked and serviced to make sure it is in good working condition, but problems are inevitable. "If the bridge gets stuck for any reason we contact the City of London police and they close the roads," says Lotter. "It's a piece of machinery and it does go wrong. You sort of half expect it, and when it does happen you really earn your money."

The senior technical officers work in rotation, with two on duty to cover the shifts of any particular day and one resting. Collectively, the shifts cover a 12-hour period from 7am to 7pm, with security staff trained to step in if the bridge needs raising at night.

Lotter has brought up three sons while working at Tower Bridge and says it works well in terms of planning. Because the days follow a very strict pattern – seven days on, three days off, seven days on, four days off – you know exactly when you will have free time. "In terms of planning it's excellent. I know when I'm working in 2015 because of the shift pattern," he says.

STOs all report to the bridge master, the person ultimately responsible for running the bridge, and each has a team of technical officers. STOs are responsible for managing the technical assistants who do everything from setting up event rooms for weddings to cleaning the old steam-powered machinery (replaced by an electro-hydraulic system in the 70s).

A lot of the maintenance and repair work is contracted out these days, and Lotter admits, somewhat ruefully, the technical officers get more opportunity to do hands-on engineering. But he adds: "Some of my job is office-based, but 30% to 40% is still engineering."

The staff all speak affectionately about the bridge – everyone seems to have a deep fascination with her. I ask Lotter if he is interested as an engineer in bridges per se, and he looks at me as though I am mad. "No, if I go somewhere and there's a bridge I might go and look at it, but I don't seek them out," he says. The message is clear: there might be other bascule bridges around the world, but none are as big and grand as Tower Bridge. She deserves special respect.

Although the bridge was completed in 1894, not all the working parts have needed replacing over the years – and those that have are expected to last a long time. The nose bolts in the centre of the bridge were replaced in 2002 – a process that took five weeks, although the bridge was not closed for the full period. "They get inspected very regularly," says Lotter. "But we would expect them to last at least 20 years. They are pretty robust."

Later we stand looking down into the cavernous area that the counter weights swing into as the bascules rise. There is apparently room to stand at the end of the hall, even when the weights are down, but no one in the bridge's 116-year history has been brave enough to try it. "You'd have to be skinny," says Lotter. "It wouldn't work for me."

The traffic passing over the bridge a few metres above our heads makes a muffled boom – 40,000 people cross over every day – and Lotter says if a ship passes by the noise is unbearable. He points out that the bridge was put together with 2m rivets – no soldering was used. "It was really over-engineered, and that's why it will remain standing for a long time to come," he says.

Curriculum vitae

Pay From £34,000 to £42,000 with London weighting. It's possible to earn a further £3,000 or so on top through overtime.

Hours Eight-hour shifts to cover the entire day, either "earlies" (7am to 4pm) or "lates" (10am to 7pm)

Work-life balance Long and often unsociable shifts can make having a social life difficult. On the other hand, you get long breaks of three or four days, sometimes in the middle of a working week, which must seem a luxury. Holidays restricted to two weeks at a time because of City of London Corporation rules.

Highs "Every day is different and offers a new challenge, whether it's dealing with contractors or the guys in marketing."

Lows "When you have to be out on the bridge on a cold winter's morning in the snow or rain dealing with a problem."