It was also felt that a new location would be more convenient for the well-to-do parishioners, mostly bankers and merchants who inhabited the mansions surrounding the Common itself.

With his local connections and popular sermons, Venn succeeded not only in drawing more people to worship at Holy Trinity but to make the church the nucleus of a radical movement that was taking hold in the 1790s.

As a committed abolitionist Venn formed part of a group of (mostly) evangelical Christians who sought an end to the practice of slavery.

This group became known as the Clapham Sect and after the death of John Thornton in 1790, his son Henry Thornton continued the group's work, which included the regular association with senior abolition figures like William Wilberforce and Granville Sharp who would come to worship at Holy Trinity.

Numerous tributes to the Clapham Sect exist within the church including a tablet designed by John Shore, Lord Teignmouth, a stained glass window, and a blue plaque which was erected in 1983 on the 150th anniversary of the Slavery Abolition Act 1833.