Game of Thrones: The sex, sorcery and slaughter continues

"We just didn't talk for a minute," says Clarke of the moment her father saw her naked on screen. "In fact, during season one I was like, 'You don't need to watch the first six episodes. Start watching from then on out.' He was wonderful about it, though. And I think he is happy that these days my clothes remain for the most part on."

Game of Thrones is now about to enter its fifth series and it casts Clarke as one of the central players, the Mother of Dragons, who is bidding to take control of the Iron Throne of Westeros.

Her character, Daenerys Targaryen, is a queen over the water, building an army to invade Westeros, which is comprised of seven warring kingdoms that indulge in political intrigue, torture, slaughter and all sorts of sexual shenanigans.

Indeed, Game of Thrones' penchant for lust and nudity does much to boost its viewing figures, although to claim that this is the only reason for the show's wild popularity would do a huge disservice to the writers, actors and their vast international fan-base. Titillation only goes so far.

The swords-and-sorcery series is a global phenomenon playing in more than 30 countries worldwide, from Bolivia to Bangladesh. "People can relate to so many characters in this show," says Kit Harington, who stars as fans' favourite Jon Snow. "People invest in this show like no other."

The drama has now eclipsed The Sopranos as HBO's most popular series of all time. The Game of Thrones' creators pitched their idea to the network as "The Sopranos in Middle Earth" and it has set records each season as viewing figures have kept growing.

In the United States, where market-share is split across dozens upon dozens of channels, the final episode of season four last year recorded live viewing figures of 9.3 million, a huge tally.

"Game of Thrones is not a niche world, like the mafia," says the Dutch actor Carice Van Houten, who has played the bewitching priestess Melisandre since her debut in the second season.

"There's a whole range of people. Young kids have big roles and very old guys have big roles. The whole of society is represented."

The average US audience during the fourth series, including catch-up services, was 18.6 million per episode, while The Sopranos' audience peaked at 18.2 million in 2002.

In the UK, the show airs on Sky Atlantic and more than two million people watch each episode, whether live or on demand, making it the highest-rating show across all of Sky's entertainment channels in 2014.

Created for the TV by David Benioff - who wrote the screenplays for the films Troy, The Kite Runner and X-Men Origins: Wolverine - along with Dan Weiss, the show draws its narrative from A Song of Ice and Fire, the ongoing series of bestselling novels by American author George RR Martin.

Martin is something of scholar as well as a novelist and has cleverly drawn from history and the best fantasy to create a brilliantly realised realm in which myriad storylines all play out together.

Westeros itself is reminiscent of these isles and the intrigue and double-dealing that underpins the battle for the Iron Throne is not too far removed from the cruel medieval turmoil remembered as the Wars of the Roses. As with the battle for the throne of England in the 15th century, Westeros sees different houses tussling for control.

"The show has amazing production values," says Iain Glen, the Edinburgh actor who has featured from the first series as Jorah Mormont, major domo to Daenerys Targaryen. There are more than 160,000 square feet of sets constructed for the show and more than 25 recurring characters.

Filming across several countries - from Iceland to Croatia, Ireland to Morocco - Game of Thrones spends longer in production each year than most Hollywood blockbusters.

"And I feel that part of its appeal is that while it's portraying a mythical past with these elements of fantasy," continues Glen, "it is very choicely done and it has a real plausibility about it.

"You look at the way people are, and how all these factions vie with each other, and how women were treated; it all feels plausible. These aspects give it a gravitas that often genre shows don't have."

This historicity is endemic and British viewers, for example, can't fail to recognise the historical inspiration for the enormous wall that runs across the north of Westeros, which bids to keep the "civilised" realms safe from the "wildings" that live in the far northern reaches (although Hadrian would have done well to construct a barrier as formidable as this construction).

Boosting the appeal of the show for Scottish viewers is the high quota of Scottish actors who have appeared in some or all of the four series so far, including James Cosmo, Rory McCann, Kate Dickie and Rose Leslie.

The show also draws on other prominent historical tribes and kingdoms - from the Mongols of the steppes to Moorish Spain - to create its lands and people.

"It is lovely to see this variety," says Jessica Henwick, a newcomer to the forthcoming series who will star as one of the war-hungry Sand Snakes from the Kingdom of Dorne.

"In Game of Thrones the lines aren't so locked in place and it is nice to see that because fantasy stories are so often derived from Greeks and Vikings and Nordic mythology. It is wonderful to be part of something that is so different."

Nevertheless, Greek and especially Nordic mythology still play a vital role; George RR Martin's world is woven with some of the most tantalising elements that imbue these great pantheons.

Like Anglo-Saxon and Norse scholar JRR Tolkien before him, Martin has a deep understanding of myth and legend, especially that of northern Europe, and draws upon magic, shape-shifting, the walking dead and mighty fire-spurting dragons.

These components are to be found in countless myths from across the globe but, as with The Lord of the Rings, here they have a decidedly Nordic flavour.

"When you look at the reasons behind the show's success, people absolutely love that fantasy aspect," says Michelle Fairley, who played the central character Catelyn Stark from the show's inception up until her surprise death at the climax to the third series.

"But then there are other people who have come across the show and then remained with it simply because of the strength of the characters. And that strength is apparent not because they are in a fantasy world, but because they are characters that transcend time and place. The issues they deal with are real ones, issues that we all might deal with in our everyday lives - loss, love, grieving, war, the destruction of a family."

The quality of the writing and acting is undeniably strong - Game of Thrones has received 42 Emmy award nominations - and the top line actors, who include Clarke, Peter Dinklage, Alfie Allen, Lena Headey, Diana Rigg, Kit Harington, Nicolaj Coster-Waldau and Maisie Williams, all transcend the genre.

"The writers have completely spoilt us," claims Clarke. "As an actor you can't read other scripts at the same time as reading Game of Thrones because David and Dan are so supremely talented that anything else just pales in comparison."

The characters they write are invariably ambiguous. "Seriously, Game of Thrones is intelligent filmmaking. To write a drama like this for 25 regular characters who have their own storylines is not an easy thing to do," says Irishman Liam Cunningham, who plays Davos Seaworth.

"The bad guys aren't the bad guys and the good guys aren't the good guys. Your empathy changes."

When it comes to moral ambiguity, the character played by Coster-Waldau is a case in point. In the first season we meet Jaime Lannister having an incestuous relationship with his sister, the powerful Cersei Lannister, played by Lena Headey.

"You first see this guy and he has nothing redeeming about him," says Coster-Waldau of his character's path through the first two series.

"One of the first things he does is push a kid [Bran Stark] out of a high window and cripple him. But slowly you learn more about him and he has more layers than you think, and good morals. He lives in a brutal world and derives no pleasure from the brutal things he does. That ultimately is one of the reasons the show is successful - it deals with basic human nature."

It is also incredibly violent; appendages of all kinds are sliced off. And like sex, slaughter sells. The writers continue to surprise their viewers, especially those that have not read Martin's novels. Even those familiar with the author's work are left guessing as the show does at times digress from the books' narrative.

The violent and surprising tone was set in the first season when one of the major characters, Ned Stark (played by one of the major actors, Sean Bean), had his head lopped off before the season ended.

"That was truly shocking," says Thomas Brodie-Sangster, who starred as Jojen Reed up until his own passing during the death-dealing finale to the fourth series. "I see Ned's as the quintessential Game of Thrones death. It set it up as a show that'd be infamous for slaughtering all your favourite characters."

Brodie-Sangster's character was a close ally of another central character, Bran Stark, son of Ned Stark, who does still live. The crippled character is brought to life on screen by Isaac Hempstead-Wright, who recalls the climax to the third season, where a whole clutch of his family - all of whom were central characters - were put to the sword, including Scottish actor Richard Madden's character Robb.

"Robb Stark's death was a massive shock and I loved the part where his killers put the wolf's head on his body and paraded the body around on a horse," he says.

The same death sequence saw the end of Catelyn Stark and Robb Stark's betrothed, Talisa, who was stabbed in her pregnant belly. Nothing in sacred and nobody is safe. "Honestly," says Emilia Clarke, "we all worry about whether our characters will be killed off."

One of the running jokes enjoyed by the two show-runners has been writing fake deaths for the leading actors, all of whom have been fooled - even Peter Dinklage, who plays arguably the series' most iconic character, the dwarf, Tyrion Lannister. Certainly, the writers fooled Alfie Allen, who plays the put-upon Theon Greyjoy.

"I remember reading a script where Bran suddenly runs out and stabs me in the heart," says Allen, brother of Lily. "I was genuinely pleased with that death - it was a great way to go - and so I accepted it and went away on holiday. I then got a phone call from David and Dan asking how I liked my death. I said I thought it was great and they said, 'How would you feel about coming back as a zombie?'

"I was like, 'OK.' And they were like, 'Great, how about a zombie with no clothes and no dialogue?' At that point I realised they were winding me up and they said, 'Of course we're keeping you on.'" Allen comes to the fore in the fifth series alongside a host of other characters, new and old.

Among the newcomers are the aforementioned Sand Snakes, who are out to avenge the death of their father, Oberyn Martell, in the last series (which was yet another jaw-dropping moment).

These three join the ranks of Thrones' strong women, who have been another major factor in the show's success. There are plenty of female role models.

Thus far viewers have rooted for lone-wolf warriors such as Arya Stark and Brienne, the sorceress Melisandre and the strong-willed rulers, Daenerys and Cersei, "but we haven't seen women like this on Game of Thrones before", says Kiwi star Keisha Castle-Hughes, who plays the warrior woman Obara.

"We are women who are strong and who collaborate. We're three girls who are violent and manipulative and who are thirsty for blood."

There seems no end to the show's appeal. "All my family love it," concludes Emilia Clarke, "even my mum, who is now calling herself the Grandmother of Dragons!"

Game of Thrones begins on Monday at 9pm on Sky Atlantic.