Season five of Peaky Blinders hasn't aired yet, but writer-creator Steven Knight is already talking about casting for seasons six and seven, the show's final two outings.

Stephen Graham, the British actor who played Al Capone on Boardwalk Empire, is being lined up for a guest role – but Knight insisted that he won't be portraying the infamous Chicago gangster again.

"We're proceeding with [casting Graham], but not for this series," Knight told Digital Spy. "Not Al Capone – I didn't want to go west. Because it's a minefield once you go into Chicago gangsters. I refer to [Capone] last series, but I didn't want to go into that."

When asked what role Graham might be playing instead, Knight replied: "I've already got it and I'm not going to tell you!"

Renowned movie actors Sam Neill and Adrien Brody have previously appeared in Peaky Blinders, but Knight admitted that in the past he has been wary of casting too many familiar faces.

"The amount of people who have come to us wanting to be in it is quite astonishing, and really good people. So what I've tried to avoid before is turning it into a 'spot the celebrity' – you know, because I think it's quite distracting sometimes," he said.

"But someone like Adrien Brody is a great actor – obviously, you want to put them in it. But I think now we're coming to the final two series, I'm going to relax and open the gates a bit because there's some amazing people who want to be in it, and I think 'why not?'"

Season five of Peaky Blinders is expected to debut on Netflix in the U.S. and BBC One in the U.K. later this year. A first look image of lead actor Cillian Murphy has already been shared, and a plot synopsis for the new season teases: "Series five of Steven Knight‘s crime family saga finds the world thrown into turmoil by the financial crash of 1929.

"Opportunity and misfortune are everywhere. When Tommy Shelby MP (Cillian Murphy) is approached by a charismatic politician with a bold vision for Britain, he realizes that his response will affect not just his family’s future but that of the entire nation.”

Who would be your dream Peaky Blinders guest star?