Happy Valley: How Sally Wainwright decided who should survive - Tommy Lee Royce or Catherine Cawood - and how Sarah Lancashire helped with finale

The final ever episode of Happy Valley was the most-watched television programme of the year so far, with 7.5 million viewers tuning in to watch the conclusion on Sunday night.

Speaking on BBC2’s Newsnight last night (Monday), Calderdale’s Sally Wainwright said she said she doesn’t often get nervous about the reaction to her shows any more but she was apprehensive about how the finale would be received.

"I tend not to get very nervous anymore about things going out,” she said. “I’m kind of philosophical that it is what it is and people will respond how they respond but I think because I’d appeared to be doing very well, I was worried that it would fall at the final hurdle and people might think it wad a disappointing ending in some way but I kind of knew it wasn’t. I knew it was what I wanted it to be.

"It was satisfying. I had a real choice to end on a pessimistic note or an optimistic one about which one of them was going to survive.

"It was a no-brainer to end on an optimistic note with someone like Catherine. She’s such a force for good.

"And I have Sarah (Lancashire) to thank for that ending in many ways because I wrote the first draft and everybody seemed quite happy with it and then she made it clear that she wasn’t happy with it.

"The Christmas before last, she came up to my house and she spent all day talking about it and she gave me some really good notes so everything got pushed a bit further in that episode and it was all thanks to Sarah.

“What was interesting for me was the actors have to get into the real granular detail of a script, because they have to learn it, and so nobody knows those scripts as well as the actors do and certainly no one knows them as well as the person playing the lead, so it was a great privilege to have the opinion of someone who knew the scripts almost better than I do because she puts so much thought into it.

"It was a fabulous conversation. She was literally here all day. It’s nice that we worked it though together.

"Her performance is just off the scale.”

Sally also explained how she is able to switch from dark scenes to moments of comedy.

"I think it’s very true to life,” she said. “I think when people are in very dark situations they do make each other laugh. The darker things are, the more they resort to not giving in to it, to cheering each other up.”

And the writer confirmed again that there will be no more Happy Valley – not even a spin-off featuring Catherine Cawood’s grandson Ryan.

"That’s it. We made a very clear decision that we didn’t want to go on and on and for it to become a pale shadow of itself.

"I think it’s good to know when to stop.”