A hundred years ago this week, Scottish socialist John Maclean delivered a famous polemic against capitalism and war from the dock of the High Court in Edinburgh.

Maclean, one of the most recognisable figures from the militant Red Clydeside era of Scotland’s early 20th century industrial history, was facing a charge of sedition for his political activity against the outbreak of the First World War.

Just months before his arrest, in reflection of his stature, Maclean had been named an honorary vice-president of the Third All-Russian Congress of Soviets and Bolshevik consul in Scotland (though the British government refused to recognise him as such).

His political work had already seen him sacked in 1915 from his job as a primary school teacher, so he instead took on the full-time task of teaching Marxist economics to working class people in Glasgow. His conclusions - that capitalist competition was the root cause of the war between Britain and Germany - saw him face frequent arrest and imprisonment.

Representing himself in the High Court on 9 May 1918 on his most serious charge yet, he delivered a 75-minute speech that has achieved an unassailable legendary status among the Scottish left.

Refusing to submit a plea, he told the court: “I wish no harm to any human being, but I, as one man, am going to exercise my freedom of speech. No human being on the face of the earth, no government is going to take from me my right to speak, my right to protest against wrong, my right to do everything that is for the benefit of mankind.

“I am not here, then, as the accused; I am here as the accuser of capitalism dripping with blood from head to foot.”

Maclean referred to the proceedings as “the most historic trial that has ever been held in Scotland - when the working class and the capitalist class meet face to face”, and used them to argue for the necessity of worldwide socialist revolution instead of war.

Ultimately, his speech failed to persuade the jury to acquit him.

A report carried in The Scotsman the next day noted: “The Lord Justice-General said a question of simple fact was submitted to the jury - whether on the eleven different occasions mentioned in the indictment the accused made the statements alleged. No attempt had been made by the defence to deny that the statements were made.

“The jury without retiring, unanimously found the charges proved.”

Maclean was sentenced to five years’ penal servitude in Peterhead. A massive working class campaign for his release gathered steam over the course of the year and eventually succeeded in securing his return to Glasgow in December 1918, not long after the end of the war.

But despite its short length, Maclean’s imprisonment took a massive toll on his health. He had committed himself to a hunger strike from July 1918 and was force-fed by prison officers twice a day; his wife said he took on “the look of a man who is going through torture”.

Maclean eventually collapsed while giving a speech in 1923 and never recovered, dying at the age of 44. His speech from the dock, delivered just a few short years prior, endures as a key part of Scotland’s political and legal history.

• A re-enactment of Maclean’s speech, organised by the Edinburgh People’s Festival, will take place outside the High Court in Edinburgh on Saturday 12 May at 11.30am.