âBigger, badder and betterâ? is how Merlinâs green-eyed monster, Morgana, describes the highly-anticipated fourth series of the hit BBC fantasy show. Katie McGrath, who plays the scheming step-sister of the heir to Camelot, is thankfully nowhere near as intimidating as her on-screen character. But she is deadly serious about the need for Merlin fans to prepare for a dark and sinister new series. I went along to the BFI last night to view the season premiere of the ‘season’ opener and was warned by PR bods that I would be âspellboundâ?. And spellbound I was.

Fear not Merlin fans, I was sworn to âkeep the magic secretâ? by an intimidating audience of die-hards and I’m not about to spoil any surprises. But it is no secret that the next series of the hit fantasy drama will be a far more shadowy affair. Love, loss, laughs and lots of handsome knights are in store for fans and the first episode, due to be screened on Ocotber 1st, did not disappoint.

Gwen (Angel Coulby), Morgana (Katie McGrath) and the man himself, Merlin (Colin Morgan), all dashed across from Wales after a long day of filming to chat to us about whatâs in store for the drama that – like the cast – seems to be growing up fast.

âThis fourth series actually feels quite different from the rest of them it feels almost like a departure. The showâs grown up, itâs more adult. Itâs still got all the fun that youâd expect from Merlin but overall in tone itâs darker and more filmicâ?, says McGrath.

The actress is so totally removed from her merciless on-screen character that I have to keep reminding myself that she is, in fact, a bitch. The end of series three left Morgana cradling her dying sister whilst letting out a deafening scream and looking like the close, personal friend of Satan. I want to know how the hell this infinitely evil sorceress can get any more…evil.

âSheâs gone from being a bubbling bitch…to being an out and out cow. Sure. But I think the interesting thing about series four is that she evolves again. Itâs been a very slow evolution from where we started to where we are now and itâs an evolution that has made sense for all the characters so for me, nothing felt jarring.â?

Merlin, a character who was quite frankly a bit of a nerd when the show kicked off, especially when placed next to the rippling muscles and jutting jaw of Arthur, also sees a transformation. The softly spoken Colin Morgan is a fan of this series, possibly because his character actually starts to get a bit cooler.

âThe good thing about it is that, as we go into the fourth series, we see him becoming the advisor and the wise Merlin that we know of old. Suddenly this knowledge is coming from somewhere within him that he probably doesnât understand. Thatâs what growing up is about.”

Angel Coulby (who plays Guinivere) is a bit cagey about revealing any major plot twists to come but I pressed her for info. Gwen and the Prince had a good old snog in front of the knights at the end of last series and, letâs be honest, itâs not as if legend doesnât give away the storyline slightly…

âThereâs definitely a bit more secrecy to come but you will see big developments. â

Any wedding bells?

âWell…their love is always there really and itâs just a question of the status issue. As long as dad (King Uther) is around itâs going to be difficult.”

Filming for series four will just be wrapping in Wales as the first episode hits our screens but the cast and crew can expect plenty more where that came from because bosses have already given the go ahead for a fifth outing, with filming expected to start in Spring 2012. Gluttons for punishment and co-creators, Johnny Capps and Julian Murphy, announced that they are also âin discussionsâ? about the possibility of a Merlin film.

But first things first. Speaking about what fans can expect from the new series, Murphy revealed: âIt is scarier but not too scary. We have been careful, but a bit of suspense never hurt anyone. The cast and their characters have grown up and the great thing about a show like Merlin is that the audience tend to grow with you.â?

The first episode provided a glimpse of the kind of windswept scenery, creepy castles and frankly terrifying ghouls who will feature in the new series and the showâs popularity has certainly afforded producers the chance to introduce some more stylish features. âWe are using a lot more green-screen this series,â? Murphy adds to impressed whoops from an excited audience, âthe actors have had to act with nothing around them most of the time!

âAnd we are also using 35mm film. For us it has a softer more magical quality that suits our show. There is a magic too it, thereâs something the light on emulsion does which no HD can touch.â?

Can we expect this to change the face of Merlin forever? Well…âbudget always comes into itâ?.

The first half of an series opening Merlin two-parter will kick series four off on BBC1, October 1st.