From a family of chimney sweeps including one of Britain’s two earliest documented Black voters, to the mystery of a 19-year-old youth believed enslaved, St Martin-in-the-Fields church on Trafalgar Square still has secrets to share as it marks its 300th anniversary.

Standing at the heart of London’s political and cultural life for three centuries, its ranks of engraved memorial stones set into the floor and walls of the crypt and cafe are yielding glimpses into long-forgotten lives of ordinary Londoners.

The Stories Behind the Stones project, which is building an online archive of the lives of those once buried in its churchyard, is part of its anniversary celebrations. These also include a free exhibition, 300 Years at the Heart and on the Edge, showcasing the church’s history as a place of activism and protest, with a focus on those “at the edge of society”, as well as a parish church and performance venue.

New research on the stones shows that William Fatt, a chimney sweep for the Admiralty and Royal Hospital Chelsea, was the son of another William Fatt, a Black chimney sweep of the king’s palaces, who voted in the 1749 Westminster byelection, making him one of the very first known Black voters.

John London had been understood to have been the first Black voter. Having cast a vote in the same election, it appears very likely that William Fatt is the joint-earliest, both pre-dating the well-known Black British writer and composer Ignatius Sancho by 31 years, according to the historian Dr Robin Eagles.

Another memorialises Richard James Said, “a native of Africa” who died aged 19 in 1810, with the inscription reading: “The Family whom he served for seven Years with uniform integrity and attention has caused this Stone to be placed over his Grave in memory of his worth and of the regret which his loss has occasioned.”

Dan Kaszeta, volunteer archivist at St Martin, said: “It’s a little bit of a mystery. He could have been a freed slave.” But, he added, the “weight of evidence” at a time when “the majority of black residents were slaves” pointed to enslavement. The stone would have cost £20 in 1810, about £2,000 today. “So these people were not poor”.

Gravestones were moved from the churchyard during development of the area, with some reused on the crypt floor and others mounted on the walls. Louisa Price, St Martin archivist, said: “We’ve got some really great stories that are emerging. By putting them all online we can make it available to others to tell us some good stories about the people who are represented here.” They also include the Huguenot celebrity physician Théodore de Mayerne, who championed free hospitals for plague victims; and Henry Croft – the original pearly king.

Art and artefacts, including a royal chair last used by Queen Mary, chart its colourful history, not just as a church used by royalty, but one which launched London’s first free lending library, and to where the origins of the Big Issue, Amnesty International and Shelter can all be traced. Its steps are a well-known site of protest, notably the anti-apartheid demonstrations of the 1980s.

The original door handle of the 1726 church, featuring a design of St Martin, a Roman soldier who shared his cloak with a near naked beggar, is on display, alongside the Lampedusa Cross, made from wood from a boat that sank off the Italian island in 2013 with the loss of 360 of 500 people on board seeking sanctuary in Europe, and now the symbol of the church’s Nazareth Community. Audio includes 1928 recordings of its choir, highlighting its history of innovation from the 1890s, when its services were relayed on the Victorian telephone audio system, the Electrophone.

Rev Sam Wells, vicar of St Martin said: “The phrase we’ve used is ‘at the heart on the edge’, so the heart refers to obviously the compassion associated with issues surrounding homelessness or since the first world war.”

That was when St Martin’s celebrated vicar, Dick Sheppard, began programmes for the area’s homeless people, coining its ethos as the “church of the ever open door”.

St Martin opened its doors to give refuge to soldiers on their way to France in the first world war. “And he turned a blind eye to who they spent the night with, which would be quite radical now, but back then was particularly embracing shall we say,” said Wells.

It formalised its fight against homelessness with the foundation of the Social Services Unit in 1948. Today The Connection at St Martin cares for about 7,500 individuals each year.

• Details of the exhibition, which runs from 24 June to 15 November 2026, can be found here