Two sisters who were codebreakers during the Second World War have spoken of their “surprise” after a portrait of them was unveiled ahead of VJ Day.

Patricia and Jean Owtram, both in their 90s, played important roles in the war but had never spoken of them, even to each other, because they had signed the Official Secrets Act.

But the pair’s recollections are featured in a book called Codebreaking Sisters: Our Secret War.

On Thursday, a painting of the two of them holding a telegram from their father, a prisoner of war (POW), was unveiled at a socially-distanced gathering at Patricia’s home in Chiswick, west London.

It comes ahead of the 75th anniversary of VJ Day on Friday, marking the surrender of Japan and the end of the war in 1945.

Speaking to the PA news agency, Patricia and Jean said: “It’s a great surprise to have a portrait painted at all because this wasn’t something we were expecting in our 90s.”

Both sisters, from Lancashire, became fluent in German after their family took in Austrian Jewish staff in the late 1930s.

After the war broke out in 1939, Patricia, then aged 18, was posted to top-secret listening stations along the British coastline where she intercepted German shipping radio.

Jean, now 95, landed a secretive role as Code & Cipher Officer in the First Aid Nursing Yeomanry and, aged 18, she was posted to Cairo, before moving on to Italy to support allied agents and aid partisan efforts against the Nazis.

Patricia, now 97, added: “What Jean and I were doing during the war was very different.

“It was years after the war before I actually got around to saying ‘by the way Jean, what were you doing in Egypt and Italy?’

“Because, as we had both signed the Official Secrets Act, we didn’t tell each other or any of our family.”

Their father Colonel Cary Owtram had been held in a POW camp in Thailand, near to the River Kwai.

Painter Dan Llywelyn Hall said the portrait took several months, and he now hopes it will be placed in a museum.

He said: “It’s a rare moment when you sit with sisters to have a shared memory of pivotal moments in history.

“The portrait explores the idea of a how a shared secret is honoured.

“Both sisters signed the secrets act and I’m interested in the moral conscience that upkeeps the lifelong private discourse.”