In more ways than one, dark clouds gathered on the habitually sunny horizons of Aidan O'Brien yesterday. For the dominant trainer of this Flat season, concerns that rain may compromise the weekend targets of his two marquee horses were secondary to the news that he is being called to account for the tactics of his pacemaker in the Juddmonte International ten days ago.

After lengthy consideration, the British Horseracing Authority (BHA) announced that O'Brien and Colm O'Donoghue, who rode Red Rock Canyon in the race won by Duke Of Marmalade, must face a disciplinary inquiry to establish if the rules regarding team tactics were breached. The Newmarket stewards did not consider an inquiry, despite the fact that O'Donoghue appeared to shift off the rail to allow his stablemate through.

Significantly, however, the BHA was at pains to emphasise that it is not reacting to those who hold the belief that the pacemaking tactics of the O'Brien stable are uniformly reprehensible. Paul Struthers, media relations manager, said: “We are satisfied there has been no other race where an inquiry should have been held.”

Struthers added that there is “no possibility” that the result - a fifth successive group one for Duke Of Marmalade - will be altered. This, though, is unlikely to relax the Coolmore ownership team, who may see the proceedings as a potential slight on their sportsmanship and, hence, demanding a vigorous defence.

The inquiry, set to be heard in three weeks' time, is likely to include high-powered legal representation, not least because O'Brien himself can be deemed guilty - and fined up to £10,000 - unless he can satisfy the panel that he instructed his rider to treat every other horse in the race without favour.

The BHA is uncomfortably aware that this is a sensitive issue. Struthers, however, explained that the authority felt it had little option, especially after comments on team tactics attributed to Johnny Murtagh, O'Brien's senior jockey.

“We are obviously conscious of the interest this will generate but it was felt that a formal inquiry had to be held,” Struthers said. “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 rule changed in 2007.”

Ironically, Red Rock Canyon is set to carry out his now regular pacemaking duties for Duke Of Marmalade in the Irish Champion Stakes on Saturday, though a repeat clash with New Approach, the Derby winner, is being jeopardised by the weather. O'Brien would be loathe to run Duke Of Marmalade on deep going - an anxiety he will extend to Henrythenavigator in the Prix du Moulin on Sunday.

One trainer hoping that the forecast rain continues in France is Richard Hannon, who has Paco Boy engaged in the Moulin. Hannon said at Goodwood: “I'd be pretty sure O'Brien's horse won't run if it's soft at Longchamp and I'd be happy to take on anything else in the race.”

Goodwood suffered an inch of rain and 29 non-runners yesterday but the resurgence of the Jeremy Noseda yard continued with group three victory for Express Wish in the Supreme Stakes.