The Split: Barcelona - What to expect from two-part special

"This is a new chapter in her life as a parent because when your daughter is getting married, you’re moving into a different phase. You know that awful phrase – ‘empty nest syndrome’?,” Walker says. “Hannah is getting close to the time when she will be in that house on her own.

“I think that she’s been very fortunate to have had amazing love in her life – from Nathan and from Christie – even though those have both collapsed.

“I think that means that she’s probably more likely to try again, but maybe with a little more realism – which is a shame, because I think as one gets older that does happen.

“I think that it’s the intimacy and the vulnerability as Hannah’s got older – it’s the idea of “do I really have the confidence and the appetite to be vulnerable with another person?

“Can I get on that merry-go-round again?” I think she’s really scared of that. When you’ve been physically intimate with someone for a long time, the idea of a new person…

“I mean that’s why Abi is so utterly brilliant. What she writes at the end for Hannah is Hannah being very, very honest – I mean I’ve not heard a woman speak like that on prime time TV before. She’s being very vulnerable, laying all her cards on the table.”

Morgan crafted The Split around the shape of three series. The idea was viewers would watch a marriage come into trouble in series one, see the passion of an affair in series two and the aftermath and consequences in series three.

“But what tends to happen with me is I really fall in love with casts and characters. What’s so interesting when you write for a cast of actors over several years is that they grow with the characters. So our actors are older, and so you want to write for them, you want to carry on to keep up with them.

“I realised what an incredible audience we have and I felt a really strong sense of fun and playfulness and a real desire to see where Hannah and the gang were now.

“And also honestly, to give the audience that we’ve grown and who are just so incredibly passionate about the show, just a lovely last…potentially last… thank you and a kind of ‘last hurrah’ treat.”

The show also follows the lives of the other Defoe sisters including Nina (Annabel Scholey) and Rose (Fiona Button) and their mother Ruth (Deborah Findlay).

Wakefield-born Scholey reflects on why the blended family resonates with audiences. “I think it's their imperfection. I think they have been written so beautifully by Abi from episode one of series one….

“They're inappropriate, but they love each other so much in that way that families do and sisters do, and I think that everybody can relate to that.

“And you know, I love my sister to bits, but we can drive each other completely insane, and that provides so much joy to watch, because everyone can identify with it.”

Morgan agrees. “One of the things that I really love about the show, and part of what gives it its rhythm and its structure, is that we always follow the rhythm of family life.

“If you look at any 12 months in a family's life, you're probably going to touch upon weddings and birthdays and car crash family dinners and holidays and, you know, crazy nights out with those that you love and break ups and make ups and loss.

“And these are universal moments that everyone will experience at some point in their lives, which is why I think audiences connect with it so much.

“What I love about The Split is that it's a drama and it's complex, and it could be dismissed as just a bit of fun, but I don't think you can ever say it's cynical.

“It’s always open hearted and warm and doesn't take itself too seriously, and is filled with joy and is filled with love. And I think that the pursuit of that is what is important in a marriage and life.”

The Split: Barcelona is available to watch on BBC iPlayer.