A boy who once set up a tiny museum in his bedroom has gone on to advise some of the world’s most famous film directors on how to make war scenes look real.

Andy Robertshaw, now 67, is one of Britain’s best-known military historians.

His job is to help directors and actors understand how soldiers lived, fought and spoke, so their films feel authentic.

He has worked on at least six major productions, including Steven Spielberg’s War Horse, Sam Mendes’ 1917, Patty Jenkins’ Wonder Woman, Peter Jackson’s They Shall Not Grow Old and Matthew Vaughn’s Kingsman: The Secret Service.

Before Hollywood came calling, he was head of education at the National Army Museum and later ran the Royal Logistic Corps Museum.

He has also spent decades excavating First World War battlefields, carefully studying the lives of soldiers through what they left behind.

Along the way he has written several books on the subject, making his research accessible to a wider audience.

Today he runs a full-size replica trench at the Kent Showground in Detling.

Using props from War Horse, he shows schoolchildren and visitors how uncomfortable and dangerous daily life was for men on the Front Line.

His first experience on a film set came in 2010 when Spielberg asked him to join the team for War Horse.

At first he was told to stay behind the cameras, dressed in plain black so he wouldn’t appear in any shots.

But Spielberg quickly decided he should be right next to the action, in uniform, to give immediate advice.

From then on Robertshaw dressed as a British officer, a German soldier or a medic, ready to step in whenever he was needed.

One example came when Benedict Cumberbatch was preparing to mount his horse.

Spielberg asked Robertshaw if the order “mount up” was correct.

He explained it had to be: “Prepare to mount. Mount!” because, as he joked “you cannot mount down.”

Sometimes the most convincing moments weren’t even scripted.

In one trench scene, a horse handler quietly told Robertshaw to warn the extras that the horse could be dangerous.

Word spread quickly, and when the animal came charging through, every man pressed himself against the wall in genuine fear.

In fact, the horse was harmless, but the panic looked so real that it stayed in the film.

By 2017, Robertshaw was working with Sam Mendes on the Hollywood blockbuster 1917.

The film was designed to look like one long continuous shot, so it required months of rehearsal and meticulous planning.

Robertshaw often walked just behind Roger Deakins, the cinematographer, ready to step in if something didn’t look right.

One detail that caught his attention was when an actor called his sergeant “Sarge.”

Robertshaw corrected them, explaining that in the British Army the word was “Sar’nt.”

“In the British Army there are only two Sarges — a sausage and a massage,” he told the crew.

In the end, though, the line stayed in the film because the team thought international audiences would recognise it more easily.

When asked which director he preferred working with, Spielberg or Mendes, Robertshaw didn’t hesitate.

“Spielberg,” he said.

“I had more involvement. I was closer to Janusz Kaminski, the director of photography, and Steven always wanted me nearby.”

Not every film he worked on was meant to be realistic.

His involvement in Wonder Woman attracted criticism from academics for inaccuracy, but he brushed it off with a smile.

“Oddly, gold armlets don’t stop machine-gun bullets,” he said.

“It’s a fantasy. You have to remember it’s not meant to be a documentary.”

On Peter Jackson’s They Shall Not Grow Old in 2018, Robertshaw was asked not to train actors but to help identify soldiers in restored First World War footage.

One scene disturbed him deeply - after a shell burst, two horses collapsed, one struggling on broken legs before being put down.

“I actually walked away from the screen,” he admitted.

“I could deal with human remains. That horse broke me.”

The moment reminded him of a dig on the Western Front where he uncovered a German soldier lying beside a small terrier.

“The dead soldier didn’t unsettle us, but the dead dog did. That was emotional.”

His fascination with history began in childhood.

During his parents’ divorce, he was taken to York, where he discovered Roman beads and began displaying them in his bedroom museum.

“My granddad said I loved playing and was good at it,” he recalled.

“I think I still am.”

That early passion grew into a career spanning museums, books, battlefield archaeology and film sets.

Now his replica trench at Detling continues the same mission, to show the public the parts of war that cinema often leaves out. The trench is open year-round, with details of open days and bookings at www.thetrench.org

“People always ask about the battles,” he said.

“But my granddad, who served in the trenches, used to say it was 9% bored stiff, 9% frozen stiff and 1% scared stiff.

“We try to show the part films don’t cover.”

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