It has been 30 years since a Highgate journalist first told the world the harrowing story of twins locked in silence with each other.

A terrifying battle of wills saw Jennifer and June Gibbons speak only to each other from the age of four – blocking out their parents, siblings and teachers – before being convicted of arson and ending up in Broadmoor as teenagers.

It was there that investigative journalist Marjorie Wallace first met the twins and found a pathway into their silent world.

The Highgate village resident, now chief executive of mental health charity Sane, said: “They were on remand and they were brought in and really looked like two coffins on the shoulders of the wardens.

“When they sat down, they didn’t lift their eyes or speak or acknowledge their father or me.

“I said, ‘You know June and Jennifer, I’ve read some of the things you’ve written, I’ve seen your diaries, I know’, and, after a while, June gave a flicker of a smile and she said, ‘Did you like them’. And from then on, they gave me the diaries.”

She went on to publish a book, The Silent Twins in 1986, telling June and Jennifer’s story.

It is once again in the spotlight as a play called Speechless, based on the book, is being performed at the Arcola Theatre in Hackney.

Tragically, Ms Wallace’s connection with the twins lasted only for the decade they were incarcerated, as Jennifer died in mysterious circumstances on the day both women were released from Broadmoor.

Eerily, they had confided in Ms Wallace just days before about a pact they had made that Jennifer should die to set June free.

An inquest was held but the reason for Jennifer’s death has never been established.

The twins were brought up near to an air force base in Wales, where their Caribbean father was posted, and both were prolific writers despite their withdrawal from spoken language.

They suffered bullying at school and a sense of isolation as the only black family in the community – thought to have contributed to their silence.

Ms Wallace went on to spend countless hours deciphering the diaries to ensure their voices were at the heart of her book.

“I feel it is one of the many, many dozens of sad and harrowing stories in which I have become involved,” said the journalist, who worked for the Sunday Times in the 1970s and 1980s and also exposed the story of thalidomide babies.

Ms Wallace was on a panel to talk about the play at the Arcola on Thursday, November 17.

It was hosted by Dame Joan Bakewell, chairwoman of Shared Experience, the company which produced the play.