SHE was the fastest and most exciting of locomotives; a green streak that connected two capital cities with ease while its guests dined in her opulent Louis XVI style carriage or sipped a martini in her cocktail bar.

The Flying Scotsman epitomises the golden age of steam, a remarkable combination of grace and power, the first locomotive to break the 100mph speed barrier and, precisely 90 years ago this year, the first to charge non-stop between London and Edinburgh.

That impressive city-to-city journey of 1928 would be revisited 50 years ago this year, in 1968, by the man who rescued her from the scrapyard; a charismatic, mutton-chopped maverick who had fallen headfirst into a lifelong love affair with Britain’s most famous locomotive when he was just four years old.

Alan Pegler – who called the Flying Scotsman his ‘old girl’ – died in 2012. Having invested a fortune in the love of his life, he ended up bankrupt, his beautiful machine tottering once again on the brink of being smashed to pieces, only this time in America.

Of course, the story would have a happy ending – today the Flying Scotsman is a national treasure.

And soon, this spectacular coal-powered titan of the train tracks will set off on another remarkable journey, one that bring Pegler’s love affair with her to a conclusion and pay the greatest of respects to the man whose lifelong devotion helped save her for generations to come.

On Saturday, October 13, the Flying Scotsman will set off from London Kings Cross bound for York, with hundreds of passengers who have paid between £150 and £330 for the return journey.

Moments after she has conquered the steep incline of Stoke Bank near Grantham, in Lincolinshire, just at the point where in 1934 she hit 100mph and made history, Pegler’s ashes will be respectfully tipped into the engine’s firebox.

Saviour and the queen of steam will become one – just as he wanted.

It will be a poignant and fitting tribute to a remarkable man whose passion for the elegant lines and powerful heart of the Sir Nigel Gresley designed Pacific LNER A-3 class locomotive ensured one of the world’s best-known steam engines would not be allowed to die.

Pegler first set eyes on her at the British Empire Exhibition in 1924, when he was a wide-eyed boy. Apple green, 70ft long and weighing 97 tonnes, her curves and imposing presence made an impression that lasted his entire life.

“He loved the Flying Scotsman,” says his daughter Penny. “She was standing there, gleaming and beautifully clean. He was lifted up to the cab; this tiny little child and this wonderful engine.

“That was the spark.”

Built in Doncaster two years earlier at a cost of under £8000, she ploughed the line between Edinburgh Waverley and London King’s Cross that was first established in 1862 as the ‘Special Scotch Express’ route.

Already a crowd-pleaser thanks to Gresley’s genius design, the Flying Scotsman entered the record books in May 1928 when a new type of tender fitted with a corridor allowed a replacement crew to take over without having to stop – enabling the first ever non-stop London to Edinburgh service.

Six years later she clocked 100mph. Never mind that No.3440 City of Truro probably did it before her, the Flying Scotsman’s run was official.

A string of shrewd marketing ideas placed her at the cutting edge of technology. In 1929 she starred in British cinema’s first talkie called, naturally, The Flying Scotsman.

In 1932 her crew spoke by telephone to the pilot of an Imperial Airways Heracles as it flew overhead, plane and locomotive powering north at 90 mph.

And the following year she raced along a two-mile track beside the river Ouse in Cambridgeshire, as a speedboat and plane attempted to outrun her. Naturally, she won.

She became a World War Two workhorse, her livery painted matt black in defiance of the Nazi threat.

But by 1963 and with diesel now replacing steam power, she was deemed surplus to requirements.

Pegler, a Nottinghamshire-born war-time bomber pilot and heir to an industrial fortune, was among the many who felt she deserved to be saved.

And a conversation in Leith, Edinburgh would give him the push to do it.

“The Flying Scotsman was a bit of a faded star by this time,” says Bob Gwynne, associate curator at the National Railway Museum in York. “And she wasn’t on the list of engines which the state wanted to preserve.

“Ramsay Ferguson, joint secretary of the Save our Steam group and Gressley A3 Preservation Society was living in Edinburgh, and met Pegler at Trinity House in Leith.

“He wanted to save her, and must have told him that they didn’t have the money to buy the Flying Scotsman. But, of course, he did.”

Pegler, who had already saved the doomed Ffestiniog Railways in Wales – now a major tourist attraction – spent £3000 to buy the locomotive he’d loved since a boy, then ploughed in thousands more for restoration work.

Proud of his new toy, he organised a patriotic tour of the United States to show her off which included a Sir Winston Churchill lookalike, tartan miniskirt clad models and actors dressed in Shakespearean garb. It boosted the locomotive’s profile even further and celebrated British engineering at a time when America was sending men to the moon.

It was such a success, that despite no longer having UK government support, Pegler decided to stage a second tour.

“It was like the best gap year,” recalls Penny, who was 17 at the time, and joined the Flying Scotsman as she powered through the Rockies, from eastern Canada to San Francisco. “He was having a great time.”

But it was expensive fun. And by the time they reached California, her father was bankrupt. Cleverly, he arranged for the Flying Scotsman to be stored within a US Army compound, guaranteeing creditors couldn’t claim her for scrap.

Pegler’s grand affair was heading for divorce. Back in the UK, Scots construction firm boss Sir William McAlpine stepped in with £25,000 to save her for a second time, and shipped her home via the Panama Canal.

Penny recalls crowds gathering to cheer her on as she arrived in Liverpool and steamed her way to Derby, just a few scratches to her famous livery to show for her trauma.

But by the early 2000s, she again required major attention. Sir William had teamed up with fellow steam enthusiast and record producer Pete Waterman, but costs spiralled and she was sold for £1.5m to Derbyshire businessman and scientist Tony Marchington.

His plans to create a Flying Scotsman Village in Edinburgh, met with a giant ‘thumbs down’ from councillors and his finances took a hit. With her again fate in the balance, a National Lottery grant and donation from Sir Richard Branson saved her for the nation.

As for her saviour Pegler, four times married and his fortune blown on his love of steam, he performed songs and talks for his passage back from America and went on to work on the Orient Express and InterCity's land cruises. He was made an OBE in 2006, and died six years later, aged 91.

Next month’s Alan Pegler Farewell outing will see his family join steam enthusiasts in plush carriages pulled by the locomotive he adored, for a final journey which he meticulously planned – even down to the exact spot at which his ashes are to become one with his beloved ‘old girl’.

The ups and downs of pursuing his great love held no regrets, recalls Penny. “It was a dream for him.

“To really live your dreams is a wonderful thing,” she says. “So many of us have dreams but do nothing about it, my dad did.”

Adds Gwynne: “He was effectively seduced by this engine and by the experiences he was having.

“He had the time of his life.”