A major exhibition opening this week in London is showcasing works by one of the most important British artists of the 20th Century. Modernist pioneer Paul Nash served as a war artist in both World Wars, and the experience left him deeply shell-shocked, as he sought to make sense of the horrors he had seen through his work.

Enter the dark and surreal world of painter Paul Nash.

This major retrospective at London's Tate Britain brings together a lifetime of the artist's work.

Nash served as a war artist in both World Wars and his experiences are recorded here in his art.

He was deeply traumatized by the horrors he experienced in the trenches of World War One.

Art critic Estelle Lovatt says Nash's paintings capture the devastation that affected him so deeply.

"Shell shock, he suffered shell shock terribly and he sought therapy through the landscape. He was so distressed after he saw what man did to nature, the firing, the battles, not just on the ground but in the air too, it left him totally distraught," said Estelle Lovatt.

His paintings are some of the most famous images from the Western Front.

Lovatt believes Nash's work serves as a warning even today.

"It is so pertinent today that we look at Nash, if Nash painted these images today - when we see in the news, the jungles in Calais, the immigrant jungles in Calais, it's horrendous what's going on - and we could learn a lesson from looking at Nash's paintings, the atrocities, the horrors, the awful waste of life that's happening through wars. You know, you can read about it in the newspaper but to come and see it captured and depicted in paintings, there's nothing more realistic," said Estelle Lovatt.

The exhibition at the Tate Britain is the artist's largest retrospective in a generation.

Curators have managed to unearth some never before seen works to exhibit to the public.

Circle of the Monoliths is being shown to the public for the first time.

It was painted on the reverse side of Nash's more famous painting The Two Serpents but is finally getting its moment in the spotlight after 80 years in the shade.

Curator Inga Fraser says the idea of a double-sided painting fits perfectly with Nash's mysticism.

"I suppose something about Nash actually makes it quite consonant that he was making double-sided paintings, he was quite a mystical person and actually had a great interest in hidden meaning, so the fact that many of his works are in fact double-sided actually goes along with his personality. However, most of the double-sided works are works that he abandoned so this is one of the rare instances of a finished painting that exists on the reverse of a canvas," said Inga Fraser.

Nash was important not just as an artist in his own right, but also for championing modern art and surrealism in Britain.

He founded the group Unit One in 1933 to promote Modernism, bringing together the artists Henry Moore, Barbara Hepworth and Edward Wadsworth.

Despite his achievements, Lovatt believes Nash was in danger of slipping off the public's radar, and is pleased his works are once again being celebrated in a major exhibition.

"He's definitely one of the most influential 20th Century British artists and I'm glad we've recognised him now and he's not been left in the way side," said Estelle Lovatt.

The Paul Nash exhibition opens to the public on October 26th and runs until March 5th, 2017.