Emma Bartholomew finds out about a radical 18th century chapel and the people who worshipped there – who are now buried in a secretive graveyard with no way in or out (except to jump over the fence like we did)

In the middle of the Morningside Estate, just behind Mead Place, a secretive walled-off burial ground is the only remaining vestige of a radical 18th century non-conformist congregation.

It centred on the Gravel Pit Chapel - which was bought by the council and knocked down in 1969 to make way for flats.

The church came to national prominence in the 1780s when Dr Richard Price, a firebrand and passionate supporter of the French Revolution became its minister.

Alan Ruston, 77, has written several books about the extraordinary congregation who did not conform to the governance of the established Church of England, and its larger-than-life leading figures. By the 19th century, Gravel Pit Chapel's congregation subscribed to Unitarianism, which offers an open-minded approach to faith and encourages individual freedom, equality for all and rational thought. Alan became a Unitarian in 1960 when he was 18.

"It was one of those things that interested me, and I became very much involved, and my face fitted," said Alan, who hadn't previously been religious, but went on to become president of the General Assembly of Unitarian and Free Christian churches in 2002.

"I liked its free and open approach," he said.

Unitarians don't have a list of things people must believe, but instead encourage everyone to reach their own conclusions. In modern times they have pressed for the introduction of gay marriage alongside the Liberal Jews and the Society of Friends.

In the 19th century Unitarianism was so radical it was made illegal itself.

Historian Alan is fascinated with the leading figures from the church's heyday, whose names are enscribed on commemmorative plaques outside the walled-off graveyard in Chatham Place where they are buried.

They include Joseph Priestley, a chemist who "discovered" oxygen in 1774. He was a minister at the Gravel Pit in the early 1790s until he had to flee for the US "because the government didn't like what he said".

Daniel Whittle Harvey, a radical politician, founded the Sunday Times newspaper and was one of the first commissioners of the Met Police. Apparently, a long procession of policemen attended his funeral when he died in the 1850s.

And Thomas Belsham - the namesake of Belsham Street behind Urswick School - was a minister from 1798 to 1804.

"He was a man who was so fat that when he went to preach in Liverpool he squeezed into the pulpit, but he couldn't get out. They had to saw him out," said Alan.

David Ricardo, the founder of the modern economic theory of rent, defected from Judaism to the congregation between 1810 and 1820, and Sir John Bowring, a writer, polymath and politician, was also a member.

"People were attracted to the free atmosphere, and it has to be said the well-known figures that were associated with it lived in Hackney Road," said Alan.

"Up until the 1850s Hackney was a celebrated place for the rich and upper classes, and it's hard to go down Hackney Road and see it in these terms, but it was very fashionable in the 1820s. But people moved out as the railways developed and the area went into decline."

By the 1960s the Gravel Pit Chapel had also gone into decline. With just six members left, it was earmarked for demolition by the Greater London Council. Alan, who was part of the administration of the London Unitarians, was drafted in because it was in "such a state".

"It was demoralising for the last minister," said Alan. "He left in 1964. We didn't try to stop it from being knocked down.

"The chapel was a large gothic building put up in 1858 and was rotting.

"They could have flattened the graveyard but they decided not to.

"It was only 42 years since the last person was buried there, and they would have had to exhume some of the bodies.

"It's very unusual that you can't get in there. It's completely walled, and there's no gate in or out.

"There has been controversy in modern times, and there have been movements to try to open it up and let it be a space for the community.

"Efforts have been made to change it but that's what it is."

Alan is giving a free talk about the Gravel Pit Chapel at 7.30pm tonight at St Augustine's Tower as part of the Hackney Society's "Talks at the Tower" series. Register at staugustinestower.org/.