Thursday brings a must-win assignment for a horse whose actual achievements are far outweighed by the volume of debate he has generated. Nothing so unusual in that - it happens in racing all the time. But the case of Twice Over is particularly intriguing because his management team are already committed to a gamble they, too, must land.

They played their hand last month after Twice Over beat the horse that was then second favourite for the 2,000 Guineas in a race traditionally regarded as the primary testing ground for that classic. He won it by travelling smoothly and knuckling down grittily, despite looking distinctly less fit than the second, Raven's Pass.

It was hard to imagine that the result would ever be different if the two met again over a mile. On previous form, Raven's Pass was just three lengths behind New Approach, last year's champion two-year-old and Guineas favourite. Although Twice Over had only ever been touted for the Derby, the leader of the second wave in the revival of his renowned trainer's fortunes would surely now contest the Guineas.

But Henry Cecil was not convinced in the immediate aftermath and neither did he change his mind on reflection. He spoke of Twice Over needing “a little bit further” than the mile of the Guineas and, presumably mindful of the colt's development for the long term, of not wanting “to go and ruin him in a race”.

This was an extraordinarily high-stakes call in a game that requires trainers to turn expensive colts into fabulously valuable stallions. Cecil declined running in a classic at a track at which his horse was proven in favour of contesting a race of far lesser prestige en route to a different classic, for which his horse has questionable stamina.

The Guineas result did little to diminish the gravity of the decision. With Raven's Pass beaten 4 lengths into fourth by Henrythenavigator, despite not being well positioned during the race, it is easy to argue that Twice Over would have finished, at the very least, third.

“Placed in the Guineas” arguably reads better on a stallion's CV than “Dante winner”. Even if he wins at York tomorrow, Twice Over must also land either the French Derby over ten furlongs or the Derby over 12 to eclipse what might have been.

Cecil will try to glean from the ten-furlong Dante whether Twice Over, whose father was a miler, has enough stamina for 12 furlongs. The skill to judge a horse's stamina requirements correctly is one hallmark of Cecil's glittering career, encompassing nine championships and a 20th-century record of 22 domestic classics.

If Twice Over fails to live up to the expectation heaped upon him, hindsight will judge his Guineas absence a career-defining chance squandered. If he succeeds, Cecil's decision will be lauded as a brave and brilliant play by an old master.

When you bet on a racecourse, it's hard to shrug off the feeling that you would have been better off watching on your TV at home, phone at hand with your bookmaker's number on speed-dial and/or your laptop displaying the latest prices from the world's leading betting exchange.

Not only is the food and drink cheaper and better at home, the prices are, too. As you comb the betting ring for 5-1 about a horse generally available at 9-2, you know damn well it's 6-1 or bigger on the exchanges, where you have to factor in commission but don't have an upper limit imposed on how much you can win.

These days the betting ring seems to function as a collection of commission agents facilitating bets between online and on-course punters, with the latter getting by far the worst of the deal.

So it's outrageously cheeky that, empowered by the Gambling Act from September 1 2007, some on-course bookmakers now bet to one sixth of the odds for a place. I have seen some do it at Perth and Sedgefield, often to the disgust of their colleagues. There are others. Of course, it is the novice racegoer who is most easily caught unawares.

The survival of on-course bookmaking is pivotal to the character of British racing but by no means assured. Those who short-change their customers risk hastening their own demise.