It seems that Happy Valley and your previous drama Last Tango in Halifax have both been genuine word of mouth hits - what response have you had from viewers?
The response to Last Tango was amazing and overwhelming. But Happy Valley has been even bigger. I've never known anything like it. People have been really impressed by Sarah Lancashire's performance. And I think it's to do with the character too - I've provided her with this character and she's really brought it to life.
Where are you at with series three of Last Tango in Halifax?
I'm writing episode five at the moment. We start filming in four weeks' time and everyone's back for the new series.
And is it true that you're taking a back seat on the fourth series of Scott & Bailey?
I've got an executive producer's credit, which means means I read the scripts and get to comment on the edit. But I'm not really involved in it at all. However, I've left it in such good hands with Nicola Shindler and Amelia Bullmore, who's taken over as lead writer.
And, finally, we have to talk about that closing scene from episode four of Happy Valley in which Catherine staggered across the street after being injured while freeing Ann - what was it like directing that moment?
It felt very emotional that these two women were helping each other like that. On the day, you're bogged down in technicalities, but at one point I did just stand by the monitors thinking, 'oh my God, Sarah Lancashire's on her knees in this street in the middle of Yorkshire'. I was blown away by her performance.
And was it your idea to have the credits roll over the sound of that crackling, beeping radio?
Yes, that came in during the edit. As soon as we put that sound on, a chill went up our spines because we'd last heard that noise when PC Kirsten McAskill had been killed earlier in the series. So we said, "well, why don't we just forget about the music and have the radio noise running all the way through the credits?" And then we asked the BBC if we could have a special dispensation so that nobody would make any crass announcements during the credits. And they agreed!
Happy Valley is released on DVD on Monday 16 June
Review: why Happy Valley is the drama of the year so far