In the mid-1970s, the Glasgow Subway was in dire need of an overhaul and Blue Peter paid us a visit to get the lowdown on the system's first major modernisation plans.
Broadcast on February 3, 1975, a special report was filmed with the long-running BBC show's legendary presenter Peter Purvis, who was treated to a 15 pence birl round the 15 stations of Glasgow's famous 'clockwork orange'.
Right from the off Purvis noted that the only thing that had changed on the underground had been the fares, with commuters still travelling in the very same carriages that were debuted when the system opened in 1896.
READ MORE: The story of the only Glasgow Subway station that no longer exists, Merkland Street
He told viewers: "There's been hardly any modernisation, the only real change being the price of a ticket - in 1896 you could travel on the railway for a ha'penny."
The special is very much of its time. Making his way down the steps of the St Enoch Underground Station, Purvis passes an advertisement offering train travel to London for just £4.75 - £35 in today's money.
Heading into the inner sanctum of the world's third oldest underground railway, it's immediately clear to Purvis that the system needs an upgrade.
"One of the first things you notice about these trains is they're rather small," says the presenter as he plonks himself down on a tired-looking leatherette seat.
"You probably noticed I had to duck my head when I got on board just now. The two carriages are supposed to hold 84 passengers sitting and standing, but as you'd expect people cram into them just like sardines."
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The fascinating footage, which has been made available online by the BBC Archive, continues with Peter Purvis wandering up to the front to speak with driver Malcolm McGregor.
The presenter learns that drivers make around 15 loops of the circuit every shift and is told about the notorious Cowcaddens bend, "the biggest problem on the track".
"Malcolm and his colleagues have to take the trains round it with extreme caution and care," says Purvis, as he sees for himself just how close the tunnel wall comes to making contact with the body of the carriage.
Purvis is also shown the rather unique maintenance methods adopted by the Glasgow Subway. In the old days, broken down trains would be shunted to the line under Govan Cross where they would then be hoisted up more than 20 feet to the maintenance depot's repair sheds.
The film concludes with Purvis explaining that modernisation plans for the system are already well underway.
Modernisation of the Glasgow Subway commenced on May 21, 1977. Dangerous and dilapidated tunnels were repaired and improved, new stations were built and existing ones enlarged and new interchanges and maintenance points meant there would be no more hoisting of stricken carriages.
"And of course," concluded Peter Purvis, "best of all [there will be] new trains."
The third major modernisation of the Glasgow Subway is now well underway, with new driverless trains - the first new rolling stock on the system since the 1977 upgrade - set to enter service later this year.
You can watch the footage of Blue Peter's 1975 visit to the Glasgow Subway here.
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