Apprentice Gina Mangan has been barred from riding rank outsider Diore Lia in the Epsom Derby and will be replaced by the more experienced junior Paddy Pilley.

After originally saying Mangan was free to take the ride on the 1000 chance, the British Horseracing Authority told her boss, trainer John Jenkins, her participation would not be "in the best interests of the sport".

Owner Richard Aylward is keen to generate publicity for Great Ormond Street Children's Hospital by running his homebred filly.

With Mangan having never ridden at Epsom nor in a big race like the Derby, the BHA said that her participation would pose an increased "risk" to the welfare of jockeys and horses.

"She's definitely running and Paddy will be riding her," Aylward said.

"Our filly is the people's champion now and I hope everyone gets behind her."

The BHA said in a statement that it was "appropriate" to accept Pilley's declaration aboard Diore Lia.

Pilley is based with Roger Charlton and has ridden 34 winners.

Mangan has ridden one winner in her career, at Roscommon in June 2009.

Pilley had success in Victoria last summer when he spent time with trainer Nigel Blackiston.

Mangan's week got even worse at Kempton on Wednesday evening when she was given a four-day careless riding suspension aboard the Jenkins-trained Alshan Fajer.

Aylward feels Mangan has been left "badly scarred" by being unable to ride in the Derby.

"She's in a terrible mess and can't work or anything," he said.

"Poor old Gina is badly scarred from what the BHA have done to her."