“I thought of myself or any of my friends going to war now, and it’s a horrifying thing to contemplate,” he says.

But if conscription was still in force, how would Radcliffe react if he were called up to fight for his country?

“I don’t know what my reaction would be,” he says. “They’d be very unfortunate to have me! It’s impossible to answer, because I don’t know what my reaction would be if that happened. I’d fight for anything I believed in passionately, I suppose. I’m sure in 1066 I would have done a really great job at Hastings!

“I think I certainly wouldn’t be able to handle myself, I’d just be too scared. There were moments when we were filming the trench scenes and it was just me and a load of shivering 18-year-olds.”

“But, equally, you can’t ever hope to fully comprehend what it was like to be there. Those men – many of them just boys – must have thought they were all going to die, and most of them did. No human being should have to go through what they went through, and that’s another reason why it’s so important to tell the story.”

On the parallels between the troops in the first world war and the troops in Iraq today: Radcliffe: "I think it would be kind of arrogant of me to comment."

On Radcliffe's great-uncle Ernie, who served at Loos, which means theoretically that Jack Kipling and great-uncle Ernie could have passed each other in the trenches: Radcliffe: "Yes, and that would be a rather remarkable coincidence. But he was one of three talismans that I had during filming. A picture of Uncle Ernie, two medals I was given as a present and a copy of Kipling's study of the Irish Guards The Irish Guards In The Great War.

"It was a pretty bizarre moment when I was told the medals had been presented to a William French, and then looked in the index in the back of Kipling's book and his name was there. You think: This man died then, at war, I don't know anything about him but he's entered my consciousness in 2007 and he entered Rudyard's 90 years ago'. And I thought that moment of shared experience was quite important."

On Radcliffe's interesting moustache: Radcliffe: "We filmed out of sequence, so I would've had to grow it back overnight, so it wasn't real, no. Another week and it would never have survived, it was seriously disintegrating "

I haven't mentioned so far what will be the biggest draw of My Boy Jack for most - that Daniel Radcliffe plays the son in his first TV role since appearing in the highest grossing movie series of all time. It's tempting to bill it as Harry Potter and the Trenches of Death (especially as Jack Kipling wears little round glasses), but unfair: Radcliffe's involvement may have helped to get the film a primetime slot, but he gives an excellent performance as a young man struggling in his father's shadow until, ironically, being sent to command troops in France. Radcliffe's many young fans may freak out at the sight of him smoking, drinking and wearing a dodgy moustache, but it may also bring them to an understanding of the First World War in a way school lessons never could.