I relish the eight-hour format of a single season because it gives you time to do that.

There [in Allied] was depicting London in the war, as well, and doing that in a way where you see something that you don't normally see, which is how hedonistic it was. In reality, that's what was going on. But, all of it worked.

What happened was I was invited to meet Tom [Hardy] to discuss a project that he had in his mind about an adventurer who returns to England from Africa with secrets and with a history, and the original idea was set some 80 years later than it is now. But in the conversation I really took to the idea and I'd wanted for a while to set something in 1830 and 1840 in London, so it struck a chord.

I'm not suggesting that ours [series] is unique in that, but they can begin to have that depth, that gravity, they can spend some time, so it's a bit more like reading a good novel, if you like.

[Allied] got the attention of (director) Bob Zemeckis and Marion Cotillard. I'm glad I waited. If it had been made 15 years before, who knows how it would have looked, but it's got the best possible cast, director and everything. It's been fantastic. It was worth waiting.

With any period piece I think the thing to do is forget that it's not contemporary when you're writing and to have the characters feel as much as possible like characters that you would know.

It has to be an actress like Marion Cotillard [in Allied] because there are so many levels to it. It's set in the Second World War, when lots of people were doing things that, outside of a war, you wouldn't do, like killing and dropping bombs. She's doing things that one wouldn't approve of, but it's war.