The seventh season of Spooks begins on 27 October with another dose of high-octane action and spy-based thrills.

Newsbeat speaks to Richard Armitage, best known as Sir Guy of Gisborne in Robin Hood, about his role in the show as an agent returning to MI5 after being imprisoned in Russia.

Were you a fan of Spooks before you got the job?
I saw the very first series of Spooks - and obviously the big chip fryer moment - and was kind of hooked from that point on. I missed the middle of series three and four, so I played catch up one night when I knew I was joining the series. I had a 48-hour Spooks-fest.

How did you get the part?
It was a bit cloak and dagger. I was approached at the end of Robin Hood in November 2007 and they said, 'are you interested?' and I said 'yeah, I am interested'. So we all got together and chatted about the potential for a character and where he would fit into this world of Spooks. It was a juggling act by the BBC to try to enable Spooks to work alongside Robin Hood, but they came out with a big tick.

You're not filming Spooks one day and Robin Hood the other?
There's been a bit of that, a bit of interchanging, which was accidental. But I had 24 hours to get from Spooks to Guy of Gisborne, which was quite interesting, but I don't think I'd have been able to have done it if Guy of Gisborne had been a new character. I would have struggled. But because I knew him I was able to go from Lucas North quite quickly.

That's sort of going from good to bad, isn't it?
It is. It's going from the white side to the dark side, but Lucas is a bit of a double-edged sword, so he's not completely white. He's a bit of a dark horse.

How much can you tell us? Are you sworn to secrecy?
There is a lot of secrecy with Spooks. There are documents locked away in safes that aren't allowed to be read by any of the cast - in the true spirit of the show...

But Lucas is a very interesting character - he's a predecessor of Tom Quinn - who worked to the top of his field and then was imprisoned in Russia and found his way back by making promises to the Russian government to work for them. He comes back to the fold and has to work very hard to be allowed to come back to MI5.

So you could be a double agent?
Yes, he could be a potential double agent, as anyone would be if they'd been away for so long. He has to be vetted quite thoroughly and you can never be sure whether you trust him because, as a character he's very ambiguous, but quite open with everybody.

But you're never quite sure if he's telling the truth or if he's joking. He makes a comment in episode one that sets things up for the rest of the series - he jokes about being a double agent. And because he jokes about it, it's like, 'well I've been honest with you now', but Harry's left thinking, 'was that a joke or was he being serious?'

And you got rid of your leather outfit from Robin Hood, didn't you?
I did. The leather's gone completely. There was a brief (from the Spooks producers) to say Lucas North wasn't allowed any leather at all, apart from shoes. So there isn't a hint of leather in this character's costume.

Were your family and friends pleased when you got the part?
Most of my friends said, 'you're gonna be way out of your depth. There's no way you're going to be able to do that!' But yeah, they were quite chuffed that I was going to be playing a spy.

Why did they think you were going to be out of your depth?
Well, you know, running around a field with a horse and a sword, and rolling over the bonnets of cars with a gun are worlds apart, so they felt I probably wouldn't be able to do that. But I think I've proved them wrong. I hope so.

Have you been doing that? Lots of running over bonnets?
Yeah, there was a shoot-out in the final episode where I surprised myself about the amount of rounds I could pull off and how quickly.

It's a weird thing. I'm not a violent person but when you put a gun in somebody's hands something strange happens. It's like a little animal comes out of you that wants to fire the gun again. I don't know what that is!

Did you have to have lessons?
I had a very, very quick lesson, but really I should have gone to a shooting range and gone through it properly, but I'd worked for weapons before on Ultimate Force. The weapons chap was the same guy so he knew that I could cope with it. But there is a procedure that you have to go through and it's very, very strict. They scare you into realising how serious the weapon is before you fire it.

What were the rest of the cast like when you joined?
They hated me! No, they were all really friendly. It was something I was worried about because going into a show that is so established I was the new boy, but they were very welcoming. And considering it's such a serious show there's a very buoyant atmosphere on set - lots of larking around and joking. Lots of fun to be had.

To get over the fact you're doing quite serious stuff?
Yes. I think in the middle of a very, very serious scene between me and Peter Firth he sort of sparkles at you and makes you corpse (break into laughter). There's a lot of corpsing - and a lot of swearing after corpsing, which is very funny! My concentration level had to double on Spooks because of those naughty people.