We've had the sham advertising entrepreneur, the failed actress and the trumped-up jockey.

Now for the "agitated goose".

Andrew Johns, one of the finest rugby league footballers there has been, a legend of his game, a hero, is to appear on Monday at an inquiry into a silly debacle that has serious, even sinister, connotations.

It is an inquiry that he, in a way, instigated.

Johns will give evidence about his role in the case of who said what to whom about the condition of the racehorse More Joyous before she ran at Randwick two weeks ago.

In a written submission to the inquiry being conducted by Racing NSW stewards, Johns admits it was he who began the "Chinese whispering" that has led to Australian racing's highest-profile trainer, and her family, being accused by one of the country's most identifiable business people of improper practices.

John Singleton claimed on national television that Gai Waterhouse told her bookmaker son Tom that More Joyous, one of the best horses in Australia, had a problem that would affect her chances in the Randwick race. More Joyous duly finished second last.

Singleton says Tom Waterhouse told Johns of the problem, Johns told the former jockey Alan Robinson, and Robinson told him.

Assuming there was a problem, the correct course of action according to Singleton, should have been for his trainer to have told him directly. But she didn't.

As it turns out, More Joyous had a minor issue that vets claim was of little or no consequence that Waterhouse didn't report, as she is obliged to.

As a result, the stewards are inquiring into what, if anything, was up with More Joyous and if there was any "insider trading" going on between the trainer Gai Waterhouse and her son the bookie.

Johns has already made a written statement to the inquiry in which he said Tom Waterhouse spoke to him about More Joyous, but did not tell him the mare was "off" as he reported to Robinson, who in turn reported to Singleton.

"I was agitated, I'd jumbled my words and now I look like a goose," Johns said in the statement.

"I said it was off, there's no way Tom Waterhouse said the word 'off'."

In an ideal world this would all have been resolved privately.

But Singleton went public before More Joyous had even been hosed down, telling the world his 30-year friendship with the Waterhouses was over, that a conflict of interest was rife between the trainer and her son and that he was sick of being treated like a "lackey" by the people he pays to train his horses.

It has since become nasty.

Gai Waterhouse, who until the inquiry began last Monday had maintained a total silence on the matter, opened up once proceedings began.

"The people involved are a beat-up jockey, a brothel owner and a footballer, and that's what's got us sitting here today. It's an absolute disgrace - you're an absolute sham, John, you really are," Waterhouse said.

Singleton has back-pedalled vigorously since race-day, and has called on Johns, someone he has known and admired since the footballer was a teenager, to "man up" and tell the truth.

"How can you be so strong on the field and so weak off it?" Singleton said of Johns in a TV interview.

"My respect for Andrew Johns has diminished massively."

Lawyer Chris Murphy, who represents Robinson, entered the fray calling Gai Waterhouse a snob and a "failed actress who married a perjurer", declaring his client had broken his neck, his back and had suffered a brain injury "riding for trainers like her".

For all the massive entertainment value in the mud-slinging and legal grappling that has accompanied it, the Singleton inquiry has turned the spotlight on a genuine issue in Australian racing: the situation in which Sydney's most successful trainer over the past 20 years is married to the most notorious bookmaker in the country and is the mother of another who is arguably the best-known fielder in the nation.

It can be likened to the CEO of a top-tier corporation being married to a high-flying stockbroker.

In racing, the situation where the country's most successful trainer is so intimately and inextricably linked to two big bookies is a fundamental and glaring flaw.

There is no suggestion, except from Singleton, that Waterhouse operates in any way improperly.

But in an industry where there are no insider-trading laws, either the world trusts that Gai Waterhouse doesn't tell her husband or son anything about her horses, particularly if they have any problems, or it doesn't.

And if it doesn't, the question of her being licensed as a trainer must inevitably be raised.