They were ordinary English women who had never met a Jew, let alone risked their lives for anyone; but with their courage and sense of justice, Ida and Louise Cook ended up rescuing dozens of would-be victims of Hitler’s death camps.

The die-hard opera fans would travel to Germany posing as tourists willing to go anywhere to hear their favourite singers. Then they would smuggle back diamonds and furs belonging to Jews to give them financial security when they arrived on British soil.

Among other tricks, the women sewed fake labels into the furs so that, if anyone asked, they could say the fabrics were English.

Their trips were funded by Ida’s career as a prolific Mills & Boon novelist, writing more than 100 romances under the nom de plume Mary Burchell. Louise’s language skills helped them communicate with the Germans.

Journalist and broadcaster Anne Sebba wrote the forward to Ida Cook’s memoirs, Safe Passage, which has recently been re-released (Ida Cook wrote it in 1950) to coincide with Mills & Boon’s centenary.

“I heard about their story and I thought it was such an extraordinary tale of eccentric people doing what they knew was right,” she says.

By the end of the war they had saved 29 people from persecution and were honoured with the title of Righteous Among The Nations by the Yad Vashem Holocaust Memorial Authority in 1965.

Nothing could have seemed less likely to the thirty-somethings Ida and Louise Cook, who lived in post-First World War england with their parents in leafy Wandsworth.

Ida and her sister spent all their earnings from their Civil Service jobs going to the opera to hear their heroes. So often did they go that they became well known in the opera world. In 1934, the wife of Austrian conductor Clemens Krauss asked the Cook girls if they would be prepared to help the many Jewish opera singers who were about to lose their livelihoods after the Nazis came to power.

They agreed, and ended up travelling to Germany from Croydon airport every week. When Ida obtained a contract with Mills & Boon to publish her first novel in 1936, she left her job to write full time and used the proceeds to pay for their charitable work.

“They went over in shabby clothes, like woollen cardigans from Woolworths, and came home with fabulous diamonds on them,” says Sebba.

“They bought a flat in Dolphin Square but instead of living in it themselves, they offered it to the Jewish immigrants who came over.

“There aren’t many Righteous Gentiles in England because we were never invaded. They didn’t have to budge from their small cottage in Wandsworth but they really put themselves in the jaws of danger,” says Sebba.

Before the operation — which grew to quite a large scale, necessitating its own bureaucracy and office — Ida had never met a Jew.

“Ida was taking the official Salzburg lecturer (who became the official Glyndebourne lecturer) around London,” says Sebba.

“On a visit to the cathedral, she turned to the woman and asked her if she was Protestant or Catholic. She replied: ‘Ida, I’m Jewish.’ Ida had no idea about this world.”

Sebba adds that had it not been for the strong sense of justice in their upbringing, the sisters may not have had the courage to pursue their dangerous mission.

Their mother’s instilling of values to the two young girls was one of the most touching parts of the story, says Sebba. “In the book, Ida says: ‘Our parents just taught us what was right.’ They just knew it instinctively.

“They didn’t have to do it. It really was dangerous. They just absolutely knew what was right. It’s terribly English, actually.”