Lily and Robert, great-grandchildren of Edinburgh-born ECHR artisan David Maxwell Fyfe, were delighted to receive the letter ahead of the opening of their show yesterday.

Sue Casson’s Dreams of Peace & Freedom is being staged by theatre company English Cabaret at C alto, Quaker Meeting House, until 24 August.

Lily is the lead singer of the performance and speaks words from the letters of her great-grandmother, Sylvia.

Welcoming the letter from No 10’s communications unit, Lily said: “A great friend of the prime minister was one of the earliest supporters of the story we tell.

“Jonathan Cooper was a wonderful human rights campaigner and brilliant barrister who was, as The Guardian said in his obituary, ‘at the forefront of efforts to decriminalise homosexuality around the world’.

“Our father first met him when he was chair of the Human Rights Lawyers Association. Jonathan loved the letters exchanged between our great-grandparents when David was a prosecutor at the Nuremberg war crimes trials.

“These letters are the foundation of our story, and we owe Jonathan a lot as his enthusiasm for them is how the PM first got to know about the story.”

After Nuremberg, David Maxwell Fyfe worked alongside Churchill to create the ECHR and with Pierre-Henri Teitgen, became one of its two ‘artisans’.

During the same years in Edinburgh, where David was born and brought up, eight groups turned up uninvited to the new Edinburgh International Festival. They were welcomed and the Fringe born.

Keir Starmer has spoken of his support for ECHR. Last July at the EPC summit at Blenheim, he said: “We will never withdraw from the European Convention on Human Rights.

“Churchill himself was among the chief architects of the Convention. It was built on the blood bond of 1945…and our shared sacrifice for freedom.

“I myself first read about these principles of the Convention and international law in a law library in Leeds, 40 years ago now. And that inspired me in everything I have done since then…

“And I still draw strength from it and value from it everyday. Because they speak about the dignity of every human being.”

Robert, who speaks his great-grandfather’s words in the show, says: “The letter from No 10 says how pleased they are that Dreams of Peace & Freedom is being performed ‘at the Edinburgh Fringe Festival, which welcomes thousands of visitors from across the globe’.

“Lily and I have grown up at the Fringe and it seems to me that both the ECHR and the Fringe are gifts from Scotland to the world.”

Lily added: “We are very grateful for the prime minister’s good wishes as our campaign to celebrate the protections of the ECHR, continues until November 4th, the date that the Convention was signed.”

For more information and tickets, visit the Edinburgh Fringe website.