Oisin Murphy missed his rides at Newmarket on Friday after failing a racecourse breathalyser test.

The dual champion jockey – who started the day 11 winners ahead of William Buick in this year’s title race, which concludes at Ascot next Saturday – had been due to have five mounts at Headquarters, including Mise En Scene in the bet365 Fillies’ Mile.

But in a post on his Twitter account, Murphy said: “I was requested to take a breath test at Newmarket today. I blew under the drink drive limit but over the riding limit.

“I’m sorry to all the people I’ve let down today. I take full responsibility. I will be riding tomorrow.”

A notice from the stewards regarding the 1.15 race at Newmarket, which should have been Murphy’s first ride of the day, read: “An enquiry was held following a report from the Equine Welfare Integrity/Collection Officer that Oisin Murphy, who was declared to ride Fiorina, had failed a breathalyser test prior to the race.

“Murphy, the Equine Welfare Integrity/Collection Officer, and Raceday Assistant were interviewed. Having heard their evidence, the matter was referred to the Head Office of the British Horseracing Authority for further consideration and Murphy was stood down for the remainder of the day.”