Jewett, 25, was arrested on Thursday morning in Cumbria on suspicion of conspiracy to defraud.

City of London police said he had been released on police bail.

Jewett is due to answer his bail on 3 July along with 27 others who have been arrested during the inquiry, including six-time champion jockey Kieren Fallon.

Fallon, who denies any wrongdoing, was among a group of people questioned when the investigation started in September 2004.

Four other jockeys - Robert Winston, Fergal Lynch, Darren Williams and Paul Bradley - along with trainers Alan Berry and Karl Burke, are also due to answer their bail later in the year.

The inquiry is examining allegations involving more than 80 races over two years.

Jewett's biggest success came when winning the 2003 Fox Hunters' Chase, known as the Amateurs' Grand National, at Aintree.

In a statement, Amateur Jockeys' Association chief executive Sarah Oliver said the organisation was "saddened" by Jewett's arrest.

"We fully support all of our members in times of adversity," she said.

"The tarnishing of his reputation can only hinder his riding opportunities, which are hard enough to come by for any amateur jockey."

Earlier, Jockeys' Association chief executive John Blake said: "We are very disappointed that another jockey has been brought into this inquiry.

"We are no further on in terms of knowing the case and the evidence against our members - as well as the other people that have been arrested.

"We are a bit confused that police need more time to consider their case in July but have made another arrest in the interim.