You've been so busy recently - do you ever feel like you need a break?
"I've been running round a lot, it's been fantastic! I kind of love what I do so I'm very lucky to be doing a lot of stuff. It's funny - when I first started as an actor, obviously there were long periods of being idle and all you want to do is work. So if I ever get the compulsion to feel like I should complain or feel like I want to take a break, I just remember how I was before and be very grateful for it."
You filmed a guest role for White Collar recently - tell us about that.
"It's the beginning episode of the third season. The show is about the FBI, who bring on a conman to help catch conmen. I play this conman who's sort of the arch nemesis of Neal, the lead character played by Matt Bomer. My character needs Neal's help to smuggle some things out of America."
Is it fun playing a villain?
"I've played a lot of villains. The villains are always fun because you can just go fractionally bigger than life. It's always a grey area because you don't want to end up moustache-twirling and making them a little false, but you always get to play a little more, whereas the lead guy has to be a little more straight."
It's a big show - what was it like working with the cast?
"It's a massive show. They're all fantastic. I was really welcomed in. There's a big sword fight in it and the fact that I'm proficient with swords really helped and everyone really respected my abilities. So it was really nice!"
And you were in Upstairs Downstairs - did you enjoy filming that?
"It was actually a weird experience for me because I went to university in Cardiff and it was shot in Cardiff. I hadn't been back to Cardiff in ten years. That's where the seed of becoming an actor was [placed] 12, nearly 13 years ago. I left Cardiff to become an actor and the next time I return I'm playing one of the leads in a big BBC drama. It was like seeing my life come full circle."
Will you be back for the new series?
"Yeah, we got contacted two weeks ago by the BBC saying that they're going to do a new series and they want Harry to return, so that's really nice. We start in October, they're saying at the moment."
When Upstairs Downstairs came out there was a bit of a public row with Downton Abbey - what did you make of that?
"It was kind of funny, because Downton Abbey was airing at the same time we were shooting Upstairs Downstairs. I've never seen Downton Abbey - not because I avoided it, it's just where I was living didn't have a TV! A lot of people on our set were watching to see how good it was and there were some people who were very nervous thinking that if they do well, we're kind of blown out of the water. But I just think audiences will always be drawn to quality television and I was applauding them, hoping they did well, because if they do well it sets a precedent and the audiences who loved that show will naturally fly onto our show. It seemed to be the case - we got 8.5m viewers every single night for the three nights, which is an incredible number of people, so I don't think it hurt us at all and all power to them. The more good drama there is out there it helps everybody, I think."
We've got to talk about FlashForward - lots of people were upset when that was cancelled. How did you feel?
"I was pretty upset. I had a long chat with [David Goyer, the creator of the show], as we were coming to the end, talking about who was my character and what was he about. They were very cloak and dagger at the beginning about giving me information - they couldn't tell me who he was or where he came from. I wasn't allowed any backstory on the character, which was difficult, trying to create the character when you know nothing about them. But the plan for the second season was we find out the reason that my character had been causing these blackouts was to cull large numbers of the population, because he'd had so many flashforwards himself he'd ended up seeing the future. The world within the next 250 years, looking at all the statistics, is going to become way too overpopulated for our natural resources. Famine, pestilence, drought - all these things will become commonplace. So as a humanitarian he wanted to indiscriminately kill lots of members of the population to try to bring the human population down. He was actually in his own warped way a good guy for humanity, which was a fascinating way to go with the second season and would have made my character one of the main characters and would be a really interesting, nefarious story. But it didn't happen, unfortunately!"
It's interesting they had it all planned out.
"Every TV show they plan so far ahead because they don't just need to know the first three or four episodes - in order to get picked up they need to know what the legs are of the show. Every show has what is called the Bible and it's everything to do with that show. I read the Bible for Lost and it's interesting - when they were shooting the pilot, in the Bible they already had mapped out what the last episode of the series was going to be."
So they had a plan - could FlashForward ever be wrapped up on TV or film?
"I doubt it now, unfortunately. Everybody's out of contract so to try to get all of those actors back at a point when they're all available and then organising all the contracts for them to come back and for that character... I mean, never say never - there are several shows that have come back after a year or two years later - but I doubt it. Which is a shame but it's the nature of the business, everybody's already moved on."
Has it made you a bit wary about joining US shows - that they can be axed so quickly?
"With British shows, because they have shorter runs they tend to know they're going to get a full season out. You get your six to eight episodes, do that and that'll be the end of it. American shows, because they have longer series, they find out four, five, six episodes in what the viewing figures are and if they're not working, they're ruthless. So it's a lot more cutthroat. But it's the same with movies, it's the same with everything. It's the unfortunate clash of the artist versus the businessman. As an artist you want to make good stories and create good art, as a businessman you want to make money and make sure the investors are happy. The two will always clash, unfortunately."
Moving on to a happier subject, for people who haven't seen your show Make It Or Break It, what's it about?
"It's set in the world of gymnastics. There's four young gymnasts who throughout the progress of the show get onto the national team, and it's all leading up to the Olympics. I play a character called Sasha who's their coach, who uses different elaborate means to bring out the best in them both as gymnasts and as young women."
What's Sasha like as a person?
"He's very guarded, he keeps his cards very close to his chest. Very few people get to know who he really is. But he's got Summer Van Horne, who's a character in there who he started developing a relationship with, and we start to get little peeks of who he is. I personally think he's a very caring, philosophical person. His bark is a lot worse than his bite!"
Why should people tune in?
"I've got a lot of friends who've tuned in just to be good friends and say that they've watched the show that I'm in, and then I get a call six months in where they say, 'I hate you, I'm hooked'. It's one of those shows where for some reason you watch two or three episodes and the drama is so good you need to find out what happens. It's just so well written, it's just a fantastic piece of drama. Plus the gymnastics in it are incredible. They've got amazing, world class gymnasts coming in and doing all this stuff, so you get to see these amazing gymnastics with a really fun story behind it."
Obviously the Olympics are coming up - do you have any plans for London 2012?
"Yeah - to not be in London! A few American friends have said, 'Oh, are you going to be over and staying with friends or your mum?' I have absolutely no desire to be round the mayhem that is going to be 2012. I think it's going to be crazy. I'd much rather sit at home and watch it on TV where I've got a good seat!"
Have you got any other projects coming up?
"As a writer I do. I have a production company and we're in development now with a feature film adaptation of Ivanhoe. I've also got two television shows and we've got meetings set up with the BBC and Sky. So lots of irons in the fire!"