An acclaimed British conductor has been fired from a prestigious American music festival after a seemingly innocent joke he made to a black friend was labelled racist.

Matthew Halls was removed as artistic director of the Oregon Bach Festival following an incident in which he imitated a southern American accent while talking to his longstanding friend, the African-American classical singer Reginald Mobley.

It is understood a white woman who overheard the joke reported it to officials at the University of Oregon, which runs the festival, claiming it amounted to a racial slur.

Shortly after Halls, who has worked with orchestras and opera houses across Europe and the US, was told by a university official his four year contract, which was to have run until 2020, was being terminated.

Mobley, a countertenor who regularly performs in the UK, has now spoken out to defend his friend, saying there was nothing racist about the joke and describing the university’s apparent treatment of Halls as deeply unjust.

“He has been victimised and I’m very upset about it,” he told The Sunday Telegraph. ”It was an innocent joke that has been entirely taken out of context.”