James Lawton: Between the horse of the moment and the one of all ages there can be just one winner - Arkle

For two days now the business has been as usual, ferocious and heroic racing, but perhaps not for 40 years has there been a wider sense in this valley that we have all been marking time. The action has been relentless but, historically speaking, the clock has stood still.

This afternoon the waiting is over when Best Mate comes on to the course in pursuit of a third straight victory in the Gold Cup, the classic steeplechase. But then in many minds the goal is so much more than that. It is not about records, not when you go an inch or two below the surface. There you see that the issue goes into the very soul of the toughest branch of equine sport.

Some say the beloved charge of Henrietta Knight, the former schoolteacher, and her husband, the gnarled old horseman and Gold Cup-winning jockey Terry Biddlecombe, can today run beside the greatest legend in all of racing - Arkle. They say that, with his fine head and beautiful stride, Best Mate can not only equal Arkle's magnificent gallop through the Sixties, when he won three Gold Cups before a tragic injury and premature death, but also touch the heart of racing in the same mystical way.

It is a belief that cannot be lightly dismissed. Even in Arkle's Irish heartland, there is growing respect for the English-trained gelding who was discovered by the legendary Irish horse dealer Tom Costello. When Best Mate ran so imperiously to take the Eriksson Chase at Leopardstown last December and sweep away doubts created by an earlier defeat, there was an extraordinary storm of acclamation.

Some likened it to the spontaneous outburst of respect that came at Old Trafford last year when the great Brazilian striker Ronaldo received a sustained standing ovation after wrecking the European Cup ambitions of Manchester United.

But are we really talking here about the kind of ground travelled by Arkle, whose owner the Duchess of Westminister swore had an intelligence that often seemed uncannily human - a horse who could flick a chocolate bar out of your pocket, open estate gates when hacked by his owner during his brief, sad retirement and strode through a paddock not as a contender but the emperor of all he surveyed?

Brough Scott, the former National Hunt jockey and celebrated broadcaster, was still an Oxford undergraduate when he rode at the 1964 Festival which marked Arkle's supreme achievement, the first of his Gold Cups which came when he shattered the huge aura of Mill House, who was trained by the great English horseman Fulke Walwyn and who a few months earlier had apparently put down the impertinent Irish challenger in the Hennessy Gold Cup at Newbury. Forty years on, Scott is still in awe.

On the eve of Best Mate's assignation with history, Scott said: "Best Mate is a wonderful horse, beautifully balanced, as perfectly made as any steeplechaser I've ever seen. But he's not Arkle. I don't think we'll ever see another Arkle, we'll never see that extraordinary, freakish ability to change the face of racing. Best Mate's supporters are right to be enthusiastic, and I think we all feel we are in the presence of something special when he goes out on to the course.

"As a young jockey and somebody who had always been besotted by horses, I just loved to see this fantastic character on the course. He didn't jig or sweat like other horses. He just marched through us with his great ears pricked.

"He was no great beauty, not as good-looking as Best Mate certainly, but you just knew there was something quite extraordinary inside him. The end, we knew well enough. It was talent and courage that simply changed the face of racing."

What Arkle did was create two systems of handicapping, one for when he ran, one for when he didn't. This is the great divide between Best Mate and Arkle, the horse of the moment and the one of the ages. Arkle won handicaps under crippling weight. He conceded as much as 33lb to top-class rivals. His heart was so strong the inconvenience was rarely noted.

Best Mate doesn't run in handicaps any more and Arkle devotees say that indeed he is coddled. When he was beaten by the ill-fated French horse Jair Du Cochet in the Peterborough Chase at Huntingdon last November, some said the price of pampering had been paid. Knight and Biddlecombe were dismissive, and it was a hard judge who did not accept that a glorious vindication had not come at Leopardstown, where Best Mate raced as flawlessly as, well, some said, Arkle.

Biddlecombe, a legendary racing figure who profited from the tragic end of Arkle when he rode Woodland Venture to success in the 1967 Gold Cup, refuses to be drawn too deeply into the debate. He makes the classic point that you can only be the best of your time, and meet the challenges that are placed before you. "What can be agreed all round," he says, "is that Best Mate is a great horse who has done great things. I don't really see the point of going much beyond that."

Yet here in Cheltenham, where Arkle has his own bronze statue, and a bookshop named for him, you cannot separate today's great race from those in which the Irish wonder ran so brilliantly in 1964, '65 and '66. Yesterday in the bookshop sales were brisk for Best Mate: Chasing Gold, by his trainer Knight, who was also available for book signing. But Arkle, who, at least physically, was not, was still achieving steady sales for his biography by Ivor Herbert. A saleswoman said: "It seems that people just can't forget the magic of Arkle."

It is magic that is overlaid by that terrible sadness of the injury at Kempton Park which ended his reign at Cheltenham, hastened his retirement and, some experts felt, set in train the arthritis that brought his early demise.

After his first rehabilitation, Arkle's trainer Tom Dreaper waited anxiously for a report from jockey Pat Taaffe, who was aboard the great horse on all his Cheltenham triumphs, after a full schooling on Naas racecourse. Taaffe recalled one of the most poignant conversations in racing history: "We pulled up. Mr Dreaper was waiting and he looked up at me with his head on one side and he asked: 'All right, Pat?' I said: 'No, sir.' He then asked: 'When do you think he'll be right?' And I said: 'I think he'll never be right, sir.'"

In just a few years, the great warrior star was dead, buried in an Irish field with a simple inscription on his gravestone: "Arkle". That, all those who had seen him beat the brilliant Mill House by five lengths, and who saw him make light of that unprecedent handicapping, was eloquent enough.

Arkle, all the millions who loved him insisted, was more than a marvellous racehorse. He was a surge of pride, a bewildering talent, an example of winning on your own terms however the world loads up its own. Best Mate, everyone agrees, is a great horse. But the race he runs today is maybe one he can never win.