Oisin Murphy, who leads the British jockeys' championship, has failed a breath test and been stood down from riding at Salisbury.

Murphy has been in excellent form in recent weeks, with his tally of 47 winners for the season putting him nine clear of Silvestre de Sousa who rode a winner at Sunday's Salisbury meeting.

Murphy was due to have five rides at Salisbury but with Royal Ascot less than 48 hours away, the stewards prevented him from riding.

"The clerk of the scales reported that Oisin Murphy provided a sample which was found to contain alcohol above the threshold level for breath samples," the British Horseracing Authority stewards' report said.

"The rider, the clerk of the scales and the sampling officer were interviewed.

"The matter was referred to the head office of the British Horseracing Authority and Murphy was suspended from riding for the rest of the day."

The alcohol level for jockeys is 17 micrograms per 100ml of breath, less than half the limit for drivers.

Murphy, who spent time in Australia as an apprentice, rode Godolphin's Benbatl to finish second to Winx in last year's Cox Plate.