Half a century ago, two pioneering examples of British transport technology were being fine-tuned ahead of their introduction to the world.

One was the Anglo-French Concorde, the supersonic jet that promised to revolutionise air travel – flying to destinations as glamorous as Barbados, Bahrain, Miami and New York – but is today just a fond, fading memory.

The other was the more humble High Speed Train, which was destined for even more exotic locales – like Peterborough, Leicester and Swansea. Its name was a real “back of an envelope” job – but unlike its more celebrated and poetically monikered rival, the High Speed Train is still around, but only just.

A symbol of British engineering flair
The Class 43 High Speed Train, or HST, appeared to modest fanfare in an era soundtracked by the Sex Pistols, the Ramones and David Bowie’s just-released “Young Americans”.

Trainspotters slipped on brown parkas to stand shivering at Doncaster station and watch “The Flying Banana” whizz by. It got that nickname from the flash of yellow on the classic wraparound InterCity 125 logo, and it dragged nationalised British Rail (BR) into the modern era. The first trains ran in 1975. Following testing, BR cleared them for their passenger debut in early 1976.

Its stub-nosed look, by legendary industrial designer Sir Kenneth Grange, makes the train look like a sad cod. But it became a transport icon. Branded InterCity 125s for their supposed top speed, they could actually hit a trifle-wobbly 148mph and were the fastest ever diesel train – and also one of the world’s fastest trains at the time.

Built in Crewe and Derby, they became emblematic of a British engineering flair which – almost – conquered the world. If BR hadn’t cancelled the HST’s sister project, the tilting Advanced Passenger Train, that too could have become a highly exportable design. But the HST succeeded and is now celebrating its 50th birthday.

After the ignominy of the Beeching cuts, BR in the 1970s wanted to focus on long-distance travel – hence the HST. The InterCity brand and refreshed design were supposed to usher in a new era of comfort and speed that would compete with cars and the 1,000 miles of motorways completed by 1972. The trains were great, the design was great, and the infamously floppy BR buffet sandwiches were… grating. You could smoke onboard and lean out of the slam-door windows.

The train of the people
HST fans are legion. Initially, trainspotters lamented the death of locomotive-hauled trains and the iconic steam services like the Flying Scotsman that came before them. But today there are plenty of aficionados. The UK HST Enthusiast Group on Facebook counts almost 14,000 members.

Travellers miss the comfort of the Mark 3 carriages they pulled – deep chairs swallowed you like a brown velour whale, and there were armrests, tables, carpets, acres of space for bags and Radio Rentals TVs and huge picture windows.

The plush interiors were a million miles away from the HST’s modern replacements, where bright neon lighting burns the retinas like it’s midday in the Nevada desert, and wipe-clean surfaces make it all look like a mobile dentist’s surgery. An hour or two on the dreaded “ironing board” seats found on newer trains will have you Googling a chiropractor.

We used HSTs to go to university in Leeds, to see great aunties in Grantham, for business in Bristol or for comedy in Edinburgh. It was the train of the people. After 50 long years of service, the HST will be taking its final bow in the South West on December 13, bringing to a close regularly timetabled service in England and Wales.

The last Great Western Railway Castle Class HSTs will retire with a flourish. Three of the last trains will line up at Plymouth Station between 7.17pm and 7.37pm for fans to take pictures.

The Castle Class trains were all named after – you guessed it – British castles. After stepping down from long-distance mainline services from London Paddington to Penzance and South Wales, they were shortened to three, four and five coaches and lived out their semi-retirement on local services ferrying cream tea-fuelled daytrippers around Devon and Cornwall.

From December 14, your only chance to ride these trains in Britain as a regular passenger will be on Scotrail’s Inter7City services from Glasgow and Edinburgh to Aberdeen and Inverness.

But it’s not the end of the line for the HST. This surprisingly resilient train will live on. Several heritage railways have bought them, and rail-tour companies use them too. The Midland Pullman runs a luxury service around Britain in a beautiful baby blue livery. Germany’s RailAdventure freight company will use them to haul cargo, while Network Rail’s canary yellow New Measurement Train, aka the “New Flying Banana”, monitors the tracks for safety.

A place in the sun
But the most intriguing part of the HST story is their glamorous second life in the sun. Like a divorced dad barrelling through a midlife crisis, the trains have pitched up in Mexico, Nigeria and Australia. An almost exact copy, christened XPT (for Express Passenger Train), was built Down Under. For a while they even used the InterCity brand too, making homesick Britons feel pangs of nostalgia. These workhorses of the Aussie rail network still run from Sydney to Melbourne and Brisbane.

They were just versions of the HST, but the real things have had a new beginning in Mexico and Nigeria. Shipped from Great Yarmouth by boat, the ex-GWR trains have travelled halfway across the world and are now well-used on services around Lagos and on the brand new Interoceanico service, which runs across the spine of Mexico from Coatzacoalcos on the Atlantic to Salina Cruz on the Pacific. This line is bizarrely run by none other than the Mexican Navy, who – one would assume – should be able to make the trains run on time.

As some HSTs head for the great siding in the sky and others enjoy a new life abroad, at age 50, Britain’s oldest train is fondly remembered as among our very best.