Why is Happy Valley such a must-see TV show? Writer and stars share why they think the BBC drama is so successful

But what makes the series such a must-see with audiences?

The BBC series first hit our screens back in 2014 and has attracted an audience of millions with the complex life of Catherine Cawood, a police sergeant in the Calder Valley.

When asked why audiences love the series so much, creator and writer Sally Wainwright said: “It’s odd with Happy Valley, so many people talk about it in such a way that I do now believe it’s pretty good! I did ask someone the other day, ‘what is it that you think?’, and she said ‘the characters and the performances and the stories’.

"You know the truth is it’s just an alchemy, just an alchemy that some shows somehow manage to press buttons with people. I guess it’s just one of those. You kind of hit a patch of gold, a seam of gold in it somehow. It does always seem to capture people’s imaginations when you are writing about things that are on the wrong side of the law.”

James Norton, who plays Tommy Lee Royce in the series, said: “Happy Valley is a must-see because you have one of the best writers in the world, at the top of her game. You have Sarah Lancashire, also an absolute legend in our industry, giving the performance of her life. An amazing cast, Siobhan Finneran and others.

"It’s just a great community, a great group of people doing great work. I just think it’s a great story, it’s a great thriller. We have got fantastic characters driving it forward. We love playing the characters because they are so beautifully drawn. And while Sally is brilliant at character dialogue, she is also extraordinary at plot.

"There is always an absolute ride, rollercoaster of a plot and many people said in the first series that they would end up behind their sofa with their hands over their mouth. I think both the second and hopefully the third deliver on that.”

Happy Valley concludes on BBC One at 9pm on Sunday