Marks senior died when his son was but nine years old, in July 1821, and the child was sent to attend Jews' Free School, where he soon emerged as a prodigy.

He supported himself by iterating Kaddish for the soul of a deceased man and reading the Bible for the blind wife of Rabbi Solomon Hirschell, thus becoming his confidant.

[2] During the 1820s, some intellectuals among Anglo-Jewry were influenced by the bibliocentric convictions of Anglican society, which regarded Testament alone as sanctified and scorned the Jews for valuing the Talmud.

Jakob Josef Petuchowski suggested these opinions reflected an old current, prevalent among the Western Sephardim, many of whom were descended from Crypto-Jews who overtly practised Christianity for generations and were unfamiliar with the Oral Torah.

Simon was acquainted with a group of members from the Mocatta and Goldsmid families, which complained over lack of decorum and was interested in praying together, rather than in separate Sephardi and Ashkenazi synagogues.

Marks' convictions suited the secessionist mainly on the practical level – while exposed to the bibliocentric ideology, most constituents never cared about it greatly but were content to abolish the Second Day, which they regarded as burdensome.

In August, Marks issued the first tome of "Forms of Prayer", a new liturgy for his flock which reflected his ideology, the remaining four parts of which were published until 1843.

The abolition of the Second Day and the new, heterodox rite alarmed the religious establishment: on 22 January 1842, a "Declaration" which served as an anathema for all practical purposes was released by Chief Rabbi Solomon Hirschell and Haham David Meldola.

Petuchowski stressed that, while the title "Reform" was sometimes conferred on the "British Jews" and some contacts between West London and the continental movement in the Hamburg Temple are attested to, they pursued a course which was its polar opposite.

In his new prayerbook and Passover Haggadah, he excised or reinstated various elements contrary to rabbinic tradition: the blessing on the Four species was changed from "who hath ordreth to take a frond", identified as such only by the Sages, to "goodly trees, palm, boughs and willows" (as in Leviticus 23:40); the Ten Commandments were read every Sabbath, a practice abolished in Talmudic times; and the blessings on lighting Hanukkah candles and reading the Scroll of Esther during Purim were rescinded, as they were not ordered by God.

Two other nonconformist synagogues left the establishment: the Manchester Congregation of British Jews adopted his prayer book but refused to abolish Second Days.