Period dramas: they’re packed full of straight, white people in stuffy outfits arguing about inheritances and proposals… right?

ABC’s new 1940s wartime drama The Halcyon is a little different. In a glamorous London hotel, you’ll find black musicians, a German refugee chef and RAF officers from across the Empire. You will find relationships that cross class boundaries, and you will find gay Londoners struggling with their sexuality.

The Halcyon itself may not have existed, but this diversity is no invention. 

“I didn't want to be in another period show that was covering the same old ground,” says Olivia Williams, who stars as snooty Lady Hamilton. “I didn't want to stand round talking about, ‘You can't marry him, his uncle is a butcher.’ I wanted to be in something dynamic.”

She adds: “The fact is, London was a diverse place in the war. That was one of the big changes that everyone had to accept is that our vast empire and the dregs of it meant that people from all over the world were pulled into it and came and fought on our behalf, and many of them passed through London and have remained largely unacknowledged for their contribution.

“I just thought it was a new angle I hadn't seen. Where it accepted that there were different people in London even then.”

Not that “hateful” Lady Hamilton is a fan of that diversity, as war and loss forces her to move from her country home to her London hotel.

“This is an uncomfortable thing for Lady Hamilton, to play someone who has to transition from a world in the country – if you like, I'm going to say it because it's the elephant in the room – the Downton world,” she explains.

“She's in the middle of the city in an urban environment with bombs dropping and people having to rub up against each other whether they like it or not.”

Fellow Halcyon star Kara Tointon has already described the series as a "sexier Downton Abbey", but Williams says the new drama will explore another side of Britain's recent history.

When she read the script, Williams immediately thought of her husband’s 101-year-old step-grandmother and her tales of coming to London in the war for the evening to dance at the Hammersmith Palais as the bombs rained down outside. She would dance all night until her feet bled with the black Canadian GIs stationed in the capital.

“When I read it I thought, this isn't just fantasy,” the actress says. “This isn't just trying to do Brookside politically correct TV. This is how it was, and it's a reflection that we don't see very often.

“And of course there were gay people! It's just that it was illegal and so everything had to be conducted in a different way. And of course there were relationships across the classes and across the races.”

Hotel manager Richard Garland may not get on with Lady Hamilton, but the actor who plays him – Steven Mackintosh – is on the same page as Williams.

"I think the kind of diversity is something that has been largely ignored, particularly in period drama," he says. "And to have some central characters that are from diverse backgrounds I think is absolutely right, and I’m sure absolutely reflects the times as they were."

It’s a lesson about our country’s history of diversity and immigration that comes at a crucial time, they both believe.

“There was a really ugly day on set, the Brexit vote happened when we were filming. Absolute devastation,” Williams recalls. The days after the vote were sobering.

“I'm married to someone who very clearly is not a native of these shores [actor and comedian Rhashan Stone], and we had the first racist remark we've experienced in our married life,” she says.

The comment? In a pub in Hampton: "I don't have to be around your sort any more."

The actress, who has starred in Rushmore, The Sixth Sense and An Education, is at pains to stress The Halcyon doesn’t have a “moral message” and won’t be shoving anything down anyone’s throats. Instead, it is a way of reminding the public of the diversity in our country's past. 

“I think parallels are very useful things, and maybe it will wake people up to it a bit and think of the consequences,” she says. “The arts have had to do that, look at Animal Farm, look at George Orwell. You have to tell the story through farmyard animals if necessary.

“Or, the other fear is, that people just go, ‘Oh I like the snotty racist bad woman. She's got a couple of great opinions.’ And then, you know, we've all failed.”

Mackintosh adds: "There’s a prescience, even more than people had kind of bargained for, in a way.

"At the beginning of our story, obviously it’s unsettling times, and it feels like unsettling times now. I mean, the world was incredibly divided then, wasn’t it? And division is everywhere now."