Secretary of Leicestershire Industrial History Society, David Lyne, explained:
"Coal is the reason the tunnel was built. In the early 19th century, Leicester tended to buy its coal from Nottinghamshire and Derbyshire, despite there being coalfields in the county.
"That was because Derbyshire and Nottinghamshire had access to the canal network, while north-west Leicestershire didn't. Pack horses brought the coal in from Whitwick, but that was slow and more expensive.
"The railway was built to address that, causing the price of coal in Leicester to plummet and the city's industry started to massively expand. This tunnel was very important for the city's industrial development."
A mile long, 4.5 million bricks were used in its construction. Yet, the tunnel is narrow: trains were much smaller than today's leviathans and the passageway carried just a single line.
It is said that when the first part of the line opened on July 17, 1832, with a train hauled by Comet – driven by George Stephenson himself, with driver Weatherburn, from Leicester – to the first Bagworth station, the locomotive's 13ft-high chimney was knocked down by Glenfield Tunnel. It is said that the train stopped so the passengers could wash themselves in nearby Rothley Brook!
But, with the decline of the railways, in 1969, British Rail sold the tunnel to Leicester City Corporation – forerunner to today's city council – for a token £5.
Today, the tunnel travels under hundreds of homes between Stephenson Court, in Glenfield and Copeland Avenue, in New Parks. There are 14 air vents along the tunnel, some of which come up in people's gardens.
At the start of the present century, a structural survey showed there was a danger of collapse, because the tunnel was not designed to take the weight of the homes built above it. The city council remedied this by spending £500,000 installing concrete reinforcements.
Sealed off for the best part of 50 years, only train-spotters and children seemed remotely interested in the vast subterranean monument to our glorious, golden age of steam. But now, you, too, have an opportunity to explore the tunnel yourself.
Leicestershire Industrial History Society are conducting tours of Glenfield Tunnel from Thursday to Sunday and again, on September 10, 11, 12 and 13. Tours of the first 100 yards are at 10am and 11.30am, then at 2.15pm and 3.30pm for 400yd tours. Booking is essential. For more information, contact Chris Hossack on 0116 241 5153 or e-mail: