21/06/2017 11:32 PM AEST | Updated 22/06/2017 9:49 AM AEST

WWII Painting That Disappeared After Churchill Ordered Cover-Up Found In Sydney

The painting is by celebrated war artist Charles Pears.

Charles Pears
The Evacuation of St. Nazaire is an important historical document for UK maritime history.

A painting which documented the deaths of thousands of British troops evacuating France during WWII -- an event which was covered up by the Churchill government -- has been discovered 76 years later in Australia.

"The Evacuation of St Nazaire" is a painting that depicts the UK's worst maritime disaster where up to 6,500 people lost their lives.

It was a tragedy the Churchill government covered up at the time. Details about the horrific number of lives lost were only made public in the last 20 years.

But then last year, the painting was found in a Sydney auction house.

Artist Charles Pears established himself as a war artist with a Government seeking to document wartime. A keen yachtsman, the sea inspired much of his work and his vast knowledge of ships and high degree of technical precision made him an ideal appointment as a war artist.

In WWI he was an official war artist to the Admiralty, before working for the War Artists' Commission during the Second World War.

Jamie Rountree from London's Rountree Tyron art gallery told HuffPost Australia "The Evacuation of St Nazaire" has been lost since it was painted in 1940.

Rountree Tryon Gallery
The Evacuation of St. Nazaire at the Rountree Tryon gallery in London.

"I assume it was lost due to the cover up, and the fact that people were not supposed to know much about the action. Churchill covered up the incident to keep morale high, as it was a significant blow to the Royal Navy," Rountree said.

But during a trip to Sydney last year, Rountree was thrilled to discover the lost Pears painting in an auction house.

"I was drawn to the painting because of its atmospheric feel and the meticulous precision with which it captured the drama and tension of the event, as if the viewer was placed in a boat edging closer to the action," Rountree said.

"Examples from these periods seldom appear on the market, as the majority are part of the Imperial War Museum and National Maritime Museum collections."

When Rountree first saw the image, he initially presumed it was of Dunkirk. But, with the aid of the gallery's maritime historian Michael Naxton, they realised it was the evacuation of St Nazaire.

Rountree Tryon Gallery
Charles Pears painting depicts the UK's worst maritime disaster with up to 6,500 lives lost .

"This gave us a serious jolt. No other paintings of this action had ever been seen, and thus this was a unique piece of WWII history that had been uncovered," Rountree said.

"I was excited to discover it was work from Charles Pears, an artist whose work we have sold for two decades, and we are delighted to have brought it back to the gallery, highlighting an important moment in UK maritime history."

According to Rountree, the painting is typical of all Pears works.

"It combines the unique stylised charm and meticulous detail he is renowned for. The scene successfully captures the drama and tension of the event, as the viewer is placed as if in a boat edging closer to the action," Rountree said.

"Owing to the Government's decision not to publicise the event and Pears' official role at the time, this is certainly an extremely rare and important historical document of a major event at the start of the Second World War."

How the painting landed in Australia is still a mystery, despite considerable research.

Rountree Tryon
Jamie Rountree from Rountree Tryon Gallery in London.

"One theory is that the Captain of the Oronsay relocated to Australia following his retirement and his family sold the painting upon his death, but we've been unable to verify this," Rountree said.

"Another theory is that the picture ended up in Australia as it was not allowed to remain in the UK due to the media blackout surrounding the events, and this perhaps is the reason that it was shipped overseas."

Now nestled amongst London's vibrant art scene, art enthusiasts can buy a slice of history when it goes on show for the first time at Rountree Tryon as part of London Art Week from 30 June - 7 July.

"We would love to see it housed in a collection, national or private, that appreciated its significance, and became good custodians of the work for future generations to enjoy. To misquote Indiana Jones: 'It belongs in a.... collection that recognises its importance'."

Charles Pears
Close up featuring details of one of the very few images in existence of the sinking Lancastria,