New generation of British actors gets its chance to shine in Game of Thrones 

Natalie Dormer as Margaery Tyrell and Lena Headey as Cersei Lannister in Game of Thrones. Photograph: Helen Sloan/HBO

Last modified on Saturday 28 February 2015 19.09 EST

When the world premiere of the much-anticipated fifth series of

takes place at the Tower of London on 18 March, it won’t only be fans queuing to find out what happens next. The red-carpet event is expected to be attended by most of the cast – and no one will be more excited than three largely unknown British actors who are set to play a major role this season.

Jessica Henwick, Toby Sebastian and Nell Tiger Free have all landed key parts in one of this season’s most eagerly awaited plotlines – events in the much-discussed but until now unseen Principality of Dorne, where a substantial part of the new season is expected to take place.

track record in spotting the stars of tomorrow – younger cast members have gone on to everything from big-budget blockbusters, such as the latest

movie, to critically acclaimed independent fare – all eyes will be on Henwick, Sebastian and Tiger Free as their characters manoeuvre their way through the always tricky politics of Westeros.

Of the three, 22-year-old Henwick, who starred in the CBBC adventure series

before playing barrister pupil Amy Lang in the legal drama

, is probably the best known. She has been cast as Nymeria Sand, one of Oberyn Martell’s daughters, a group of not-to-be-messed-with warrior princesses known as the Sand Snakes.

movie [unconfirmed reports suggest she has a role in that film] – so I knew her pretty well,” says

casting director, Nina Gold. “We knew she’d be a good fit.”

Nell Tiger Free is one of three new young British actors appearing in the new season of Game of Thrones. Photograph: Simon Webster /Rex Features

Relative newcomer Sebastian will play Oberyn’s nephew, Trystane Martell, and is better known as a flamenco musician, though he has a small part in the forthcoming action comedy

“We knew Toby more because he’d done a lot of music things in the past, but he has a really romantic feel that just worked,” says Gold of the striking young actor, whose part is thought to have been significantly changed from the books.

The third member of the British trio, 15-year-old Nell Tiger Free, takes on the role of Cersei Lannister’s daughter Myrcella, last seen being sent to Dorne as part of a political marriage deal. She replaces Aimee Richardson in the role; no explanation for the change has been given. “Nell is really brilliant,” says Gold. “We’d seen her in [indie film]

and she had a great natural style. She’s a very talented young actresswho’s going to go far.”

has been celebrated for its astute casting of young unknowns, most notably Maisie Williams and Sophie Turner who play the show’s beleaguered Stark sisters, it’s not averse to the odd piece of big name window-dressing. Earlier seasons have seen the likes of Diana Rigg and Charles Dance take key roles and this season’s star catch is Jonathan Pryce, hot off his turn as Cardinal Wolsey in

, which Gold also cast, and playing a very different man of faith with a mission that will have lasting repercussions for many in the capital of King’s Landing. “Now and then we have the opportunity to cast someone with more of a profile,” says Gold. “I’d say each season we get one really great well-known actor, and getting Jonathan was really satisfying because he’s someone I’ve always wanted to cast.”

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The other piece of eye-catching casting is that of former child star Keisha Castle-Hughes, Oscar-nominated at 13 for

, who will play the oldest Sand Snake, Obara. Castle-Hughes reportedly pushed for a role because she was a fan of Martin’s books – and Gold admits they are inundated with requests from people desperate to appear. “We do get amazing messages from fabulous people saying they’d like a part – I saw Danny Dyer saying he’d been turned back three times. I honestly don’t remember that but he must have been. People are really keen to be on the show.”Not surprisingly, given the boost it can give a career. Former

star Jerome Flynn banished two decades’ worth of Robson & Jerome memories with a swashbuckling turn as cynical mercenary Bronn, while established stars from Stephen Dillane to Iain Glen have carved out a part of Westeros to call their own.

“We have so many conversations where we say, ‘Oh he’s very

but what role?” Gold admits. “Generally we’re looking for people who are going to bring something original to the part. With Jerome he hadn’t been that keen to do stuff for a while, but the character and the world really appealed to him. Similarly, [Scottish actor] Rory McCann really took his character [the tormented royal bodyguard Sandor Clegane] and made it live.”

Does she worry about getting it wrong? “We get a pretty good brief and then it’s largely about instinct. Young actors are a risk because there’s so much growing up and developing to do, and the men are generally harder because those parts are so unlike 21st-century men. The trickiest was probably Oberyn Martell. We try not to get wound up by negative feedback and [Chilean actor] Pedro Pascal was really successful in the end, but he was the hardest to cast.”

Seasons one to four of Game of Thrones are currently available on demand through Sky Box Sets and NOW TV

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