The glass floors have been installed on both the 120-year-old bridge’s two high-level walkways – the second is scheduled to open on December 1.

This week’s first visitors understandably looked a tad nervous at the prospect of stepping out – but those with a head for heights will be rewarded with breath-taking views of the Thames and passing traffic. If they’re lucky they’ll also be able to see the bridge opening from above.

The £1m project has involved the installation of glass floors measuring 11m long and 1.8m wide in each walkway. Each floor comprises six glass panels, each three inches thick and weighing around 530kg – more than enough to bear the weight of the plumpest tourist.

“There is that sense of trepidation,” Chris Earlie, head of the Tower Bridge Exhibition, told The Guardian. “It is more exciting I think because you are not actually that high, you can see everything in detail beneath you. I do a lot of climbing and adventure sports but, even for me, the first time was a bit difficult.”

Rectangles of oak flooring and Victorian carbon steel removed during the construction process have been carefully stored in case there is ever a wish to restore the bridge to its original condition.

Tower Bridge opened in 1894 to ease traffic congestion. It uses powerful mechanisms called bascules to raise and lower the road at either end in about 10 minutes so that ships can pass through. The upper walkways were included so that pedestrians could continue to cross the Thames while the bridge was raised.

Some concerns have been expressed that the glass floors could also afford some interesting views for thrill-seekers looking up from below, or for those up top seeking happy reflections. However, strategically-placed lighting should ensure that neither women in skirts nor Scotsmen in kilts necessarily require underwear.

Adult admission to the Tower Bridge Exhibition costs £9. Further details are available by visiting www.towerbridge.org.uk