Jeremy Corbyn encapsulated everything that was deceitful about his campaign to be leader of Her Majesty’s Opposition when he claimed he wanted to prioritise “the needs of the poor and the human rights of us all”. From the point of view of the poor and the oppressed, his words were a grim joke.

Like many from the Left’s dark corners, Corbyn does not believe in the human rights of “us all”. He is concerned only with the rights of those whose oppression is politically useful. If the oppressed’s suffering can be blamed on the West, he will defend them. If not, he is on their enemies’ side.

A short and far from comprehensive tour of the regimes Corbyn has supported includes the geriatric Cuban dictatorship, the corrupt and extraordinarily incompetent Chavistas who have come close to bankrupting oil-rich Venezuela, and Russian imperialists who have used force to redraw Europe’s boundaries.

You will not understand how a sickness on the Left has spread from the fringes to the mainstream, unless you pause, take a deep breath, pour a stiff drink and contemplate the strangeness of that list for a moment. In the 20th century, it would have had a kind of coherence. Cuba was then and remains a Communist country. Far-leftists, and indeed many who were not Marxists, placed the Castro dictatorship’s record in providing healthcare above its record of denying democratic rights, human rights and trade union rights. Their refusal to confront oppression may have been scandalous. But they were socialists so you could understand how they could reserve their condemnations for fascistic or conservative regimes. No one in the rich world took much notice of Venezuela before the millennium. But if you had explained that a socialist party would take power, jail opponents and restrict press freedom, they would have understood that the same double standards would apply to Chavez. As for Russia, our time travellers would assume that by “Russia” Corbyn meant the Soviet Union, and once again, they would have slotted his support into traditional notions of Left and Right.

The malaise on the modern Left becomes evident only when you remember what century you are living in. Russia does not pretend to be socialist now. It is a dictatorial kleptocracy, whose oligarchs stash their stolen money in Mayfair, Saint-Tropez and Palm Beach, and whose leader sends his armies over Russia’s borders to grab the territory of neighbouring states. Putin boasts to the world that he wants to be the leader of its reactionary and illiberal forces. He is committed to adventurism and the repression of minorities, particularly homosexuals. Modern Russia is the heir to the Tsarist empire, which 19th-century liberals and socialists feared above all other powers.