Tower Bridge behind the scenes

The bascules of Tower Bridge are currently stationary. As part of the current renovation, the bridge will not be lifted until early April - unfortunate for vessels wishing to pass through it, but lucky for those of us able to take tours behind the scenes. Tower Bridge Exhibition took the opportunity to offer regular engineering tours, including the chance to wander inside a bascule chamber.

We began our tour on the upper walks of the bridge, however. Originally, these were built as a means for pedestrians to continue crossing the bridge while the roadway was raised. However, given that opening and closing are pretty quick while there are a lot of stairs to the higher level, this route was never very popular. It became the haunt of prostitutes and suicides before being closed altogether in 1910. Now accessible once more as part of the Tower Bridge Exhibition, it offers views up and down the river as well as exhibitions on the bridge's history.

At road level, we went into the former control room. Today, the bridge is raised by buttons rather than these elegant levers. However, even the Victorian system for controlling the hydraulic machinery had built-in failsafes. The bridge would not open if the various operations were not carried out in the correct order.

The final stage of the tour took us properly backstage: down into an engine room and one of the bascule chambers. We saw one of the old lifting engines, which like the control room was full of gleaming metal and intriguing parts. Alongside it, the modern machinery is altogether more prosaic. Originally, a large steam engine (the final stage of our visit) pumped water into six accumulators. These kept the water under pressure until it was needed to drive the lifting engines. Today, each modern lifting engine does the job alone.

We walked further down, past one of the accumulators, and into the bascule chamber. 'Bascule' means 'seesaw', which explains how the bridge-raising works. A counterweight falls as the roadway lifts, and that counterweight sweeps into this space below the road. However, it doesn't make the grooves in either side wall: nobody is quite sure why they are there.

Our tour ended in the engine rooms generally open to the public. Here is the pumping engine which used to feed the accumulators. More bright and gleaming Victorian machinery awaited us; as I left and walked back over the bridge, it was with a new appreciation of this marvel of Victorian engineering and architecture.