“The leader is Castle Falls, with Rutherfords along the inside. And he’s been … And Rutherfords has been hampered, and so has Castle Falls.

Rondetto has fallen, Princeful has fallen, Norther has fallen, Kirtle-Lad has fallen, The Fossa has fallen, there's a right pile-up.

Leedsy has climbed over the fence and left his jockey there.

“And now, with all this mayhem, Foinavon has gone off on his own.”

Sixty-seven words delivered in twenty seconds that shaped the history of a Grand National and television commentary as Michael O’Hehir’s narrative for the BBC captured the pivotal moment of Foinavon 100-1 victory in the 1967 National.

O’Hehir was a commentator and broadcaster in Ireland for nearly 50 years and his range included covering the funeral of President John Kennedy in

1963 but this was different. Forget gravitas, this was about explaining gravity and its effects upon jockeys when the riderless Popham Down veered dramatically to his right at the 23rd fence bringing most of the field to a standstill.

O’Hehir would later recount how his preparation, in the days when there were no graphics of colours available, had stood him in good stead.

“I stand for about an hour before the National, checking off each jockey’s colours as that jockey gets on to the scales. It means one thing on paper but to actually see the colours – the shade of blue, the tinge of red – it can make all the difference,” he would later recount.

“But I saw this man, standing in the line of jockeys, with a black jacket and yellow and red braces. And I went down my list and I couldn’t make out what’s this.”

It was John Buckingham, who had picked up the ride on Foinavon after three other jockeys had turned it down. “I said ‘Johnny, what’s this you’re riding?’ ‘I’m riding Foinavon’ he said, and I said ‘when that ran at Cheltenham it had light green and dark green quarters?’”

Foinavon’s owner thought that green was unlucky and had decided upon another set of colours and thus O’Hehir’s eye for detail saved him when the horse nobody fancied emerged from the slate-grey gloom.

Fifty years on Richard Hoiles, who will lead ITV’s commentary team for this year’s race, will be making his own history as only the fourth commentator to call the finish of the race on national television and he is in no doubt about the quality O’Hehir’s performance.

“It was an amazing piece of work,” Hoiles said. “I don’t know if he used a monitor but it would’ve been in black and white. At one point there’s literally no other words other than the horses going down. Then he picks Foinavon getting over so there’s no other pause in the commentary.

“In those circumstances you could be excused a pause while you’re trying to work out what’s happening. But it’s seamless and by far the most underrated racecourse commentary, I think.”

Hoiles and his fellow commentators will doubtless settle for a seamless performance on Saturday.