On Expenses (BBC4, 9pm)

BRIAN COX has played historical characters before but they’ve usually been dead. In BBC4’s On Expenses, though, he’s playing someone very real and very alive – former Speaker of the House of Commons, Michael Martin.

The one-off drama tells of journalist and campaigner Heather Brooke (played by Anna Maxwell Martin) whose tenacious investigations brought about the disclosure of MPs’ expenses.

“You feel a big responsibility to get them right – but you’re playing a view of the man, it can’t be the man himself,”

says Cox, of playing a real character.

“But I actually was empathetic towards Michael Martin. I remember that voice he had – ‘Order, order’ – that slightly funny way of speaking, which was kind of self-conscious, and I always found him a touching character.

“I was out of the country at the time the scandal broke and suddenly they were all turning on him and I remember thinking, ‘why?’. I started out with great empathy and, in the end, I was quite sympathetic.”

He thinks that clearly Martin made errors in the way he handled the situation, but there’s never been any precedent for that kind of thing, and he was totally out of his depth.

“That was the sad thing about it,” says Cox. “And, of course, he was an old trade union man and he kind of went back to that model in terms of his handling of the situation, which wasn’t quite what it needed. It needed something a little more statesman-like.

“He was a traditionalist and he’s a Catholic and he’s got all those Catholic values, and I think he is a very good man.

He was a kind of fall guy. He was quite proud and made errors, but it was a very unusual situation and, in the end, his situation was a tragic one.”

Cox wanted to play his humanitarian side. “There’s also something very comic about him as a character – in those gowns, which he actually wore rather well. It was a very sad situation, really, and he believed in Parliament, he believed in the process of Parliament and he did believe people did things for the best things. There was a lot of dissolutionment.

It must have left its mark on him.

‘HE was genuinely trying to close Pandora’s Box and, once that’s opened, it’s very difficult to close. He did say it was a legitimate way of topping up salaries – by claiming legitimate expenses – but, of course, human beings always abuse systems and that’s where he was very naive.”

Anna Maxwell Martin knew nothing about Heather Brooke before taking on the role. “I really wanted to play a strong, independent, spirited woman, which is who Heather is, and that’s really what interested me,” she explains. “After I accepted the role I met Heather, really just to gauge what she was like as a person. I wasn’t trying to do an impression of her in the drama, but I felt it was important to meet her and get an impression of who she was and what she was like.

“And it was very nice. We got on very well and had a really good chat.”

The fact that Heather isn’t hugely known made it easier for her. “You could go on YouTube and find her, but she’s not famous – people don’t instantly know who she is – so I didn’t feel that pressure of having to do an impression of her. I thought it was more important to tell her story,” she says.

“So it was great to meet Heather and it did help me but, for me, it was about the writing and finding the truth within every scene that we played with my fellow actors.”

As Heather dances in her spare time, she had to do some dancing for the cameras.

“The disco-dancing was absolutely hideous and horrifying in every way,”

says the actress.

“There wasn’t much time for me to learn how to dance before shooting, so that was pretty terrifying. I’m used to singing and things, but I’m not a dancer.

I gave it my all but it was nerve-racking.”