On 15 April 1918, Maclean was arrested for sedition. He was refused bail and his trial fixed for 9 May in Edinburgh. He conducted his own defence in a defiant manner, refusing to plead and when asked if he objected to any of the jurors replying, "I object to the whole lot of them." The prosecution case was based on the testimony of witnesses who had attended his meetings, who quoted extracts from his speeches using notes they had written up from memory after the meeting. Maclean objected to his words being taken out of context, saying. "The main parts of my speech, in which my themes are developed are omitted. I want to expose the trickery of the British government and their police and their lawyers."