The Clyde Tunnel is actually two parallel tunnels. Works started in 1957 and the tunnels cost £10.5m; with the builders using a tunnel shield based on the design that Marc Isambard Brunel used to burrow beneath the River Thames a century earlier.

With the tunnel workings pressurised, to stop the weight of earth and water above from caving them in, many workers got the bends - just like deep-sea divers. This was also down to some workers refusing to to go through the decompression sequence given the length of time required (around an hour) – as they came back to the surface. Two men died of the condition

The first tunnel was opened by the Queen in 1963, and the second opened the following year.

At the time it was the steepest road tunnel ever built, with a maximum gradient of 1:16 (6%). Today it carries around 25 million vehicles a year.

Now, let's see if you can hold your breath all the way through...

--

If you are interested in purchasing one of our products but live outside of the UK please get in touch.

--

The Herald Picture Store is proud to present these images in their actual condition. We haven't manipulated these photographs and are proud of their character.

Please be aware that due to their age some images may show imperfections. This is as a result of the technology available at the time they were captured and/or scanned and saved for our records.