Mark Johnston has become the most successful racehorse trainer in Britain, having saddled his 4,194th winner on Thursday.

After weeks of anticipation, the decisive success came at York in which Frankie Dettori rode 20-1 shot Johnston’s Poet’s Society to victory in a one-mile handicap.

It is an extraordinary achievement for a man who started out with no family connection to horse racing and bought his first stable with an endowment mortgage and £5,000 in cash from his in-laws. His first winner was Hinari Video in July 1987 at Carlisle. During the celebrations that night, Johnston’s TV was set to the racing results page on Teletext, there being no way to watch the race again in those days of four channels and no internet.

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The record was held by Richard Hannon Sr, who retired five years ago, having held a licence for 43 years. Johnston has taken 31 years to set a new bar, though there are now many more races each year than when Hannon started out.

“He was also a great believer in running his horses,” Johnston has said of Hannon. “He had a big team and ran them a lot. Some people would have tried to belittle the numbers and said they were not as important as the quality, but to my mind you’ve got to do both. Certainly, if I was an owner, I wouldn’t want my horse in a yard where the chances of it never running, never mind winning, were fairly high, and that does apply to a lot of yards.”

There has been plenty of quality during Johnston’s career, including a 2,000 Guineas with Mister Baileys, while Attraction won the 1,000 Guineas in both England and Ireland. But the 58-year-old would like more Classic success before passing on the operation to his son Charlie, and suggested recently that he had had fewer runners in the Derby during his whole career than the Irish trainer Aidan O’Brien might have in a single running.

He has named Shamardal as the best horse he trained, though, under the terms of his association with Sheikh Mohammed at the time, he only had the colt to the end of his juvenile season. Shamardal was unbeaten in three runs for Johnston and won the Dewhurst before joining Sheikh Mohammed’s main trainer, Saeed bin Suroor, and landing the French Derby the following year.

“Throughout the time I trained Shamardal, I never considered the opposition,” Johnston said recently. “When you’ve got a horse like him, the opposition’s of no concern.”