How did you get involved in the project?

I actually went up for Sexby, but obviously ended up playing Rainsborough. John Simm is fantastic as Edward Sexby, so as soon as I heard that he was playing him, I thought "Yeah, that's cool." And Rainsborough's a really interesting character, so it just went from there.

Did you know much about the English Civil War?

I knew about Cromwell, having grown up in Ireland. I was aware of the destruction, the way he laid waste to Ireland, and that he was against the Catholic Church, but I didn't actually know much about Charles I and the beheading, and the Roundheads and all the internal politics going on within the revolution. Rainsborough was almost like Lenin, a radical revolutionary 300 years before. He wanted to get rid of the monarchy and of the entitlement to vote through nobility and lineage. He felt every man should have the vote and everybody should be free, and should have a say in the running of their country. And Cromwell just thought that was crazy. Rainsborough was quite a dangerous man to have about.

Do you think this part of English history has been undervalued?

I never knew that there was any of this sentiment in 17th-century England, with people fighting for the freedom of all men. They just wanted to sweep out the whole system. It would have been very interesting to see what would have happened if they'd got their way.

How important do you think Rainsborough was in fomenting rebellion?

Well, Cromwell definitely needed him. They may have had different opinions, but they both wanted to get rid of the king. There were a few really important figures - John Lilburne was another - each of them brought support, including soldiers to fight for the cause. And Rainsborough brought with him his naval background as well, because he used to command a ship in the navy. In fact, his men turned against him and mutinied, because the Levellers weren't too popular in the navy.

Were you comfortable with the mix of fact and fiction in this drama?

What's great about this series is that it deals with all the politics and the historical aspects, but it's got something to drive it on so it's not just about politics and history. Throwing in this high-spirited woman is brilliant and the men that she beds - and by God she beds quite a few. But it's a great vehicle to take an audience through.

Your new film, Hunger, is also about to come out. You play Bobby Sands - you're making a bit of a habit of playing anti-establishment figures...

It seems to be so, yes! Michael Collins, then Rainsborough, then Bobby Sands. It's not intentional; it's just worked that way.

You had to lose a lot of weight to play Sands. Did you then have to put it on to play Rainsborough?

Yeah. We finished Hunger in January, and then I went to Australia for a month to eat and recover, before filming this. The weight came back on really quickly; it didn't seem to be a problem. And it was a lot more fun putting it back on that taking it off, that's for damn sure!