History has not been kind to Lord George Gordon and deservedly so. His name is indelibly linked to the infamous anti-Catholic “Gordon riots” which swept London 240 years ago this month.

But there is a twist in the tale of Lord Gordon: although associated with Protestant fanaticism, he ended his life a convert to Judaism.

Raised on his aristocratic family’s Scottish estates, Gordon entered parliament in 1774 and swiftly sunk into obscurity. His speeches, the historian JA Cannon has suggested, were “extravagant, incoherent and irrelevant”.

But in the passage of the 1788 Catholic Relief Act — which partially lifted the various repressive measures enacted against Catholics — he happened upon a cause which brought him the fame and recognition he sought.

His campaigning for repeal of the act — an act which he had originally neither spoken nor voted against — led to the London Protestant Association choosing him as his president. Gordon proceeded to deliver increasingly irate warning about the threat of “popery”.

It was thus perhaps inevitable that when, on 2 June 1780, Gordon led a crowd of 60,000 people to Parliament to present a petition against the act, violence would ensue. While Gordon and the Protestant Association desperately attempted to put the genie of anti-Catholicism they had unleashed back in the bottle, London saw days of rioting, disorder and unrest. Catholics were attacked and their homes, schools and chapels looted and destroyed. Newgate and other prisons were stormed and the Bank of England came under assault. As troops attempted to restore order, more than 200 people were killed.

Gordon was taken to the Tower and tried for high treason. A jury, however, took a mere half an hour to find him not guilty on the grounds that he had tried to quell the violence and that, as his defence team put it, he had not “wickedly and traitorously preconcerted [sic] and designed it”.

Gordon’s parliamentary career was over but his combination of erraticism and outspokenness was sooner or later liable to land him in trouble with the law once again. In 1787, he was convicted of libelling the French envoy in London, Queen Marie Antoinette and the English judicial system, and sentenced to five years in prison. His conviction came in the same year that he converted to Judaism, taking the name Israel Abraham George Gordon.

His commitment to his new faith was indisputable. “This singular proselyte,” wrote James Picciotto in Sketches of Anglo-Jewish History, “was very regular in his Jewish observances in prison. Every morning he was seen with phylacteries between his eyes and opposite to his heart; every Saturday he held public service in his room with the aid of ten Polish Jews.”

Gordon now began to experience some of the prejudice which he had previously been blind to when it was directed at Catholics. At a court appearance in 1793, he refused to take off his hat but the judge ordered it forcibly removed. “He became,” [the historian Colin] Haydon has suggested, “the butt of antisemitic prints and ballads, depicting his conversion as further proof of his insanity.”

Nonetheless, his time in prison — he died in Newgate at the age of 42 in November 1793 after contracting typhoid — was, Cannon believes, “perhaps the happiest period of his life”.

In his novel Barnaby Rudge, which is set against the backdrop of the riots, Charles Dickens writes of Gordon: “The prisoners bemoaned his loss, and missed him; for though his means were not large, his charity was great, and in bestowing alms among them he considered the necessities of all alike, and knew no distinction of sect or creed. There are wise men … who may learn something, even from this poor crazy lord.”