Jockey Johnny Murtagh has been ordered to attend a disciplinary hearing on Thursday alongside trainer Aidan O'Brien and rider Colm O'Donoghue.

The inquiry into Duke of Marmalade's Juddmonte International Stakes victory has been broadened to include Murtagh.

The British Horseracing Authority (BHA) has summoned the trio to attend over a possible breach of team tactics rules in the Newmarket race on August 23.

O'Donoghue was riding the pacemaker Red Rock Canyon in the Group One event.

The BHA will examine whether he rode deliberately to help Murtagh, on stablemate Duke Of Marmalade, win.

O'Donoghue's mount moved off the rail, allowing Murtagh to take the gap and eventually claim the race.

In a surprise development, it emerged on Tuesday that triple Epsom Derby winner Murtagh has also been called to the inquiry.

A panel will consider whether the 38-year-old, number one rider to Irish champion trainer O'Brien, has breached rules in that he "instructed, directed or encouraged O'Donoghue to ride in the way he did".

O'Donoghue must answer a charge that he made "a manoeuvre in the interests of a horse from the same stable."

Duke of Marmalade's triumph was one of 20 Group One victories so far this season for champion Irish trainer O'Brien, who is chasing a world record 26.

O'Brien will have to satisfy officials that he "instructed his rider to treat every other horse in the race without favour."

In the aftermath of the race, the BHA had indicated Murtagh would not face disciplinary action.

BHA spokesman Paul Struthers said at the time: "We are obviously conscious of the interest this will generate but, having reviewed the video and read comments attributed to Johnny Murtagh in the press, it was felt that a formal inquiry into the incident had to be held.

"This will ensure that the matter is considered thoroughly, fairly and openly.

"This is the first time we have reviewed a race for a possible breach of 'team tactics' since the rules changed in 2007 and we are satisfied that there has been no other race where an inquiry should have been held.

"I would also like to make clear that there is no possibility of the result of the Juddmonte International being affected."