Rupert Grint says we're in a golden age of television and that he's pleased Sick Note is his first TV project.

What drew you to Sick Note?

The scripts are really clever and funny, and it's a very fresh idea. I hadn't read anything in a long time that had made me laugh out loud like this. Dark things have always appealed to me. I don't know why - perhaps I have a bit of a sick sense of humour!

The idea of lives spiralling further and further out of control is a great basis for a show. All the characters are covering something up. That gradually becomes clearer. It makes for an interesting dynamic where everyone is concealing the truth.

What have you enjoyed about Nat Saunders and James Serafinowicz's scripts?

Sick Note is brilliantly written because it has so many twists and turns. You never know where it will go next. I love the spontaneity of it. Also, the director Matt Lipsey is great. He lets us go off script, and it feels very free. Nat and James are rewriting on the hoof. It is a very collaborative process.

Tell us a bit about Daniel...

He has become completely immune to lying. He's lied all the way though his life. He's always faking some sort injury to get off work, and his relationship is hanging by a string of white lies. He's lost his passion for everything - his job and his relationship. He is really hitting the wall. He's jaded, and he's happier watching Game of Thrones and playing PlayStation than going to work. Life is slowly passing him by.

What happens next?

Daniel suddenly gets the worst news possible when he is diagnosed with a terminal illness. But he doesn't come clean when he realises he's been misdiagnosed because everything is so much easier for him when people think he is ill. Suddenly he is not completely invisible anymore - people are noticing him. He also manages to save his relationship. All of a sudden, he gets a burst of life that he's never had before.

Why doesn't he reveal that, in fact, he's not ill?

When Daniel finds out that he's not terminally ill, he has a big decision to make. It's not easy for him. He is aware that it's a terrible, terrible thing to do, but he feels he has no choice because everything is going so much better. Now he's got everything he wants. He thinks his hand has been forced.

Are there any similarities between your own life and Daniel's?

The main thing I could relate to was that I've always been quite philosophical and laid back.

What's the relationship between Daniel and Dr Glennis?

Sick Note is a classic farce, and Daniel and Iain are almost a Laurel & Hardy kind of double act. The doctor is completely incapable of anything. He makes it so much more difficult to keep the lie secret because he is constantly cocking it up. Daniel is continually frustrated by Iain because the doctor has no concept of the consequences and the gravity of the situation they're in.

What has it been like to work with Nick Frost?

It's been brilliant. But it's also been very challenging trying to keep a straight face. He's absolutely hilarious. He keeps trying to make me 'corpse'. He's always coming out with things during filming. They stay with you all day, and you can't forget them. He makes it very difficult, but it's been great working with him.

Do you worry at all about the subject matter in Sick Note?

No. Daniel genuinely thought he had cancer - that was completely real. Things just got out of hand. And he's not just flippantly doing this because he can. He's always very much aware that it's a terrible, terrible thing to be doing.

Are there any big differences between making film and TV?

No. I don't see huge difference. We're in a golden age of television. It's great to have the opportunity to develop a character like Daniel over several hours - that's hard to carve out in a single film. Also the shooting style on Sick Note is very free.

Daniel is very different from the role for which you are best known, Ron Weasley in the Harry Potter films. Did you deliberately choose a character so far removed from your most celebrated part?

No. It's not a conscious decision to show my versatility. Of course, you do feel a pressure after something like Harry Potter. You want the chance to show that you can do different things. And it's refreshing to work without CGI and on a smaller budget. I love the fast pace of this filming. But Harry Potter was never something I was desperate to shake off. I just enjoy doing different things.

Finally, how would you sum up your experience of making Sick Note?

It's been amazing. This is the first TV I've ever done, and I've loved every minute of it!