In a statement, he said: "I wish to announce that I have tested positive for a banned substance that may signal the end of my riding career.

"It is well known that I have put a great deal of effort into my ongoing recovery but life is not always as easy as it often appears."

Gallagher's admission comes in the wake of UK Sport's quarterly anti-doping report, which revealed that four jockeys had tested positive for banned drugs.

Gallagher has endured a turbulent career and four years ago he was arrested - but never charged - as part of police investigations into race-fixing and doping.

Following a 14-month fight, he cleared his name but the ordeal took its toll and in July 2000, Gallagher was given a six-month ban from racing after a positive test for cocaine.

The 32-year-old Gallagher conceded he must take responsibility for his actions.

But he added: "I wish to stress that during the past two years I have been drug tested on over 300 occasions and this has been the only positive test.

"Also, I have been tested 12 times in the past month since the positive sample, all of which have been negative.

"I know that I will be banned from riding for a significant period and a return to riding is unlikely at this stage.

"I will try to maintain a career in racing despite this devastating news and I remain committed to my recovery.

"My only request is that I be allowed some space and privacy to rebuild my life and support my young family.

" I did not want or intend for my riding career to take this course and I regret my actions."