The year 1656 is usually remembered as the date of the readmission of Jews to England. But something else happened then, regarded by some as an infamous act that remains a lingering stain on European Jewry.

Amsterdam's Sephardi authorities pronounced a cherem, a ban of excommunication, on the rationalist philosopher Baruch Spinoza.

Spinoza, one of the greatest Jewish minds, was condemned for his "evil opinions" and "abominable heresies". A free-thinker ahead of his time, he rejected the idea of a personal God, the divine origin of the Torah, the chosenness of the Jews and the immortality of the soul.

Such views might seem unexceptionable to many today and might even be held by some Progressive rabbis. But in the 17th century, they would have been an outrageous challenge to the religious establishment, Jewish or Christian. Even though Spinoza published his unorthodox
ideas only after the cherem, it is assumed that he must have been talking about them before.

Every so often, calls have come from those who champion Spinoza as an intellectual hero for the excommunication to be reversed. In the 1920s, the Hebrew University historian, Joseph Klausner - Amos Oz's great-uncle - declared, "The sin of Judaism against you is removed."

A new attempt at rehabilitation has recently been made by the successors of those who cast Spinoza out of the fold. In September 2012, the executive of the Portugees-Israëlietishce Gemeente te Amsterdam asked their rabbinical head, the Haham, Dr Pinchas Toledano to reconsider the cherem after consulting a number of international Spinoza scholars.

In their appeal to the Haham, they argued that the cherem was "in painful contrast to a key value of the modern world, where we consider 'freedom of speech' as a fundamental human right".

The academics were divided on overturning the ban. Dr Piet Steenbakkers, of Utrecht University, thought "it would put to rest a vexed issue and… be a homage to an original thinker of whom the Portuguese-Jewish community has reason to be proud".

But the Hebrew University scholar Yosef Kaplan argued that history cannot be changed, that he could not think of any Orthodox rabbi who would agree to annul the cherem and in any event it would be a "pathetic and preposterous gesture".

After reviewing the scholarly opinions, Rabbi Toledano - who is former head of London's Sephardi Beth Din - decided to let the cherem remain. His ruling, although issued last year, has only lately begun to circulate. While the cherem was "shrouded in mystery" because no explanatory documents had been deposited in the congregation's archives, he noted that, significantly, the cherem had not been lifted in the philosopher's lifetime. Normally rabbis would lift a cherem in 30 days.

"Beyond any shadow of doubt, Spinoza never requested to rescind the cherem," Haham Toledano stated.

"Spinoza should have come before the Beth Din and asked for forgiveness - and then (and only then) the cherem would have been annulled. The fact that he has been buried in a non-Jewish cemetery shows clearly that, to the last breath of his life, he was indifferent to the cherem and that he never asked for forgiveness or did teshuvah [repentance] by retracting publicly what he had said about God and his contempt for Chazal [the Sages]."

Rabbi Toledano went on: "The moment we rescind the cherem, even if we could, it would imply that we share his heretic views… To him, the Law of Moses was not Divine and no longer relevant after the destruction of the Jewish state. To him there was no God, except in a 'philosophical' sense. How on earth can we even consider to remove the cherem from a person with such preposterous ideas, where he was tearing apart the very fundaments of our religion?"

The Haham also observed, in response to the executive's point about freedom of speech, that Judaism did not share such a concept. Did free speech mean, he asked, that "we in our synagogue should spread the denial of God's existence to the extent that it destroys our heritage and the pillars on which Judaism rests"?

Spinoza may remain formally excluded from the house of Israel. But what about his writings?

As Dr Kaplan pointed out, in 1953 Israeli Chief Rabbi Isaac Herzog concluded that there was in fact no prohibition on modern Jews reading them.