Downton Abbey star Dan Stevens has cautioned over being judgemental about unconventional relationships.

The actor, who has been married to singer Susie Hariet since 2009, is currently starring in a film about a couple who decide to sleep with other people before spending the rest of their lives together.

He told the Press Association: “It’s not to say that traditional relationships are wrong, or to brand anything in a particular way, but to challenge those ways of thinking can still be healthy.

“The fact is that our generation more than any, and perhaps the generation before, know that some of those so-called traditional relationships are in fact are quite toxic.

“I think being stuck in a mode is not always the healthiest thing.”

Stevens praised the openness of people younger than him, saying: “I think this generation going forward, the younger generation coming up, the way they are looking at relationships and even gender fluidity and sexuality is so radically different to how our parents’ generation looked at it.

“It’s amazing to see how these ideas are evolving.”

Stevens said Permission, in which he stars opposite Rebecca Hall, stemmed from conversations amongst his group of friends about open relationships.

Dan Stevens with Rebecca Hall in Permission (Good Deed Entertainment)

He said: “It was a chance for a group of friends to get together and really play out a story that had come together out of conversations that we had been having, either amongst ourselves or with our friends for probably about 10 years.

“Brian [Crano, the writer and director] had gathered these stories, and some of the bits of the story are based on things that friends of ours have tried or people we know have tried.”

He added: “I’ve certainly known people who have opened up their relationships and it’s kind of fascinating when you talk to people about that.

“The other thing Brian introduced me to was the Savage Love podcast, which I started listening to probably about 10 years ago as well, and that is a very eye opening, mind-expanding thing to listen to.

“You suddenly realise however dramatic or otherwise you think your own life is, you start listening to other people’s angle on things and it really does expand things.”

Asked if the film had challenged his own ideas about relationships, he said: “Yeah, I mean if you’re honest about your relationship, you should have that challenged on a regular basis I think.

“I don’t think many of my ideas are that fixed in stone, it’s something as a group of friends that we have always talked about and I hope the film encourages other people to think about things in a different way.

Permission is available now on iTunes.