Racing Victoria stewards have issued charges under Australian Rules of Racing against jumps jockey Paul Hamblin and McNamara following an investigation into the performance of Hornets' Nest in a hurdle at Casterton on June 29.

The stewards alleged Hamblin's riding of Hornets' Nest was contrary to rules in that he failed between approximately the 1200m and the 800m mark to improve his position and maintain contact with the field. They also alleged that between approximately the 800m mark and jumping the last obstacle Hamblin did not ride his mount with sufficient vigour to improve their position. The stewards also allege that McNamara's instructions to Hamblin prior to the race contributed to Hamblin's breach of the rules.

McNamara said he had handed in his trainer's licence after he spoke with stewards on Monday.

"I'm totally shocked that I've been charged," the Koroit milk bar owner said.

"I don't want to be associated with an industry or anyone who calls me a cheat. I don't want to be involved in an industry that sees other people doing things wrong constantly and all they get is a slap on the wrist.

"The allegation has left a very bad taste in my mouth. I'm just walking away from the industry. I feel very sorry for Paul. He's totally innocent of the charge."

Hamblin, who has been riding for more than 30 years and rates his 2015 Galleywood Hurdle win on Stand To Gain as one of his career highlights, said he was devastated with the charge.

"I'm not sure where my career goes now," Hamblin said. "There's no way that I would pull a horse up. People can look and they will see Hornets' Nest ran the same as he did at Casterton in his next start in the Lafferty Hurdle. The seriousness of the charge is extremely worrying."

The charges will be heard before the Victorian Racing Tribunal on a date to be fixed.