Epsom Derby: Gina Mangan is barred from riding Diore Lia
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|Dates: 2-3 June Big races: Oaks 16:30 BST, Friday 2 June; Derby 16:30 BST Saturday 3 June Coverage: Commentaries on BBC Radio 5 live; results and reports on BBC Sport website|
Racing's regulator the British Horseracing Authority (BHA) is to bar inexperienced apprentice jockey Gina Mangan from riding rank outsider Diore Lia in Saturday's Epsom Derby.
Diore Lia was a 1,000-1 shot for the race and Mangan has only ever ridden one winner - Roscommon in 2009.
Prize money was to be donated to Great Ormond Street's children's hospital.
The BHA said it had "a responsibility to place the welfare of our participants, equine and human, first".
A statement added: "While risk can never be removed entirely, it is possible to identify factors that can increase risk, and act on them.
"While Miss Mangan has held her licence for a number of years she remains inexperienced, with only 69 rides and one winner to her name. She has never ridden at Epsom and certainly never ridden in a race on the scale and stage of the Derby, with all the unique challenges it presents.
"We believe that the decision is the correct one in the best interests of all concerned and the sport. Should the BHA have not acted and an incident have occurred, then the disappointment of one rider could have been placed in stark contrast with the potential consequences."
'We're in the Derby to have a go at it'
The total purse is set to be £1.625m, the richest race ever staged in Britain, with the winner receiving £920,913 and prize money then paid down to sixth place, which will net £21,922.
Owner Richard Aylward said he would now refuse to run the horse.
He told the Racing Post: "We've had people donate tonight from America to the charity, all on the grounds of the horse being in the race. We're in the Derby to have a go at it, and the BHA has been got to. They've changed their mind."
BBC Sport horse racing correspondent Cornelius Lysaght
There are two ways of looking at this.
On the one hand, the owner's paid the entry fee, the run is for charity and Mangan is technically qualified for what has the look of a romantic, 'David against Goliath' sporting encounter.
On the other, the most famous flat race in the world is no place for an inexperienced apprentice, and she could blight the race.
The authority has decided, probably correctly, that the risk of a drama is just too high.
Unlike the Grand National, there are no jumps, but this race too is a considerable test of all involved.