UNTIL last year, Lesley Manville had remained rather under the radar.

The 63-year-old, who was born in Brighton, had worked for decades in theatre, TV and film, perhaps most notably in Mike Leigh movies such as All Or Nothing and Another Year.

But it was when she was nominated for an Oscar, for Best Supporting Actress, for her role in 2018 film Phantom Thread, that she was really thrust into the limelight.

The part she mainly gets recognised for though, she says, is BBC Two comedy Mum, which is returning for its third and final season, and sees her play the titular character, Cathy.

“For me, this job has been a really big deal,” notes the actress, who has one son with her ex-husband, actor Gary Oldman (who was also up for an Oscar last year, for Best Actor, and ended up winning).

“It feels very significant, because of all the ingredients being so good - the writing, the directing of Stefan [Golaszewski], the directing of Richard Laxton, who did our first series, all of the cast, just extraordinarily good actors.

“That cocktail is quite rare.

“And then you make it and it has a resonance with viewers, it touches them.

“It’s part of a great wave of new comedy that’s around at the moment, which I think is just such a golden time that we’re in.”

Mum follows Cathy as she tries to move on from the death of her husband, Dave.

But this new series is a little different.

Instead of being filmed in Cathy’s house, she is away for a week with the family and each of the six episodes covers a different day, as they stay in a country house for her brother Derek’s birthday.

Undoubtedly, the storyline that people will be most excited about is the developing relationship between Cathy and old friend Michael (played by Peter Mullan), after she finally admitted her true feelings for him in the last series.

In the first episode, it becomes apparent that the two are closer than ever (although Cathy is worried about her son, and Dave’s parents finding out, because Michael and Dave were best friends).

Manville thought the way the blossoming romance was revealed to viewers was clever.

“You could have had us in bed with our hot chocolate and pyjamas but it’s not, it’s just one fleeting kiss on the lips and you think the audience is probably going, ‘Got to rewind.’”

The actress continues enthusiastically: “But the other thing that is so good, I think, is it’s a story about middle-aged people falling in love and, very sweetly, a lot of the time just looking like teenagers because this whole new fizzy thing is happening to them.

“That’s not dealt with very much in telly and films. Or, in Hollywood, it’s all kind of, ‘Aren’t they still sexy at 50?’ - but it’s all glamorous, and they’ve all still got to look great.

“It [Mum] is real, it’s normal, it’s the unglamorous thing about being with somebody for the first time, or the relationship being new.

“Cathy and Michael are such secure people, it doesn’t matter that Michael turns up and sees her in her worst mum jeans, and terrible slippers.

“None of that matters, and that’s very refreshing.”

Mum has been a huge success, raking in three nominations for the 2019 Bafta TV Awards: Best Female Performance in a Comedy Programme for Manville, Best Male Performance in a Comedy Programme for Mullan, and Best Scripted Comedy for writer Golaszewski, who previously penned Him & Her, starring Russell Tovey.

The sitcom has also attracted a very loyal fanbase, “but it’s interesting the kind of response that it gets”, notes Manville.

“It’s always quite gentle.

“People are not going, ‘Oi, Cathy.’ It’s quiet, and it’s ‘We love Mum’ and ‘What’s going to happen?’ - as if you’re going to tell them.

“But, yeah, it’s been quite remarkable really.”

Perhaps one reason why the show has resonated with viewers so much is because the characters seem like people we probably all know in real life.

As well as matriarch Cathy - “She’s very non-judgmental, very patient, with a huge sense of humour of her own and a twinkle” - there’s gentle, laid-back Michael; ditsy, chatty Jason; his equally ditsy, chatty girlfriend Kelly; bumbling Derek; catty Pauline; and the grumpy parents-in-law Reg and Maureen.

“When we first got going with Mum, it was finding that balance, with all of us really,” Manville says of developing the relatable characters.

“It was finding that ground where you can play them and place them absolutely properly, and it took some time.”

It’s also a show that mixes comedy and drama so very well - expect to get teary at least once or twice while watching.

Does Manville get emotional while filming scenes?

She nods emphatically. “I remember in series 2 when Michael comes in to tell Cathy that his mother’s died overnight, and Cathy’s rabbiting on about tea bags, and keeps asking if he’s all right, and he can’t quite say it.

“And when Michael finally says ‘My mum died’... I think it was hard for all of us. You do get involved, you get drawn into what the character is thinking but you get moved on some other level as well, especially because Peter was so heartbreaking.

“You can’t help but well up.”

Manville is, understandably, careful not to reveal exactly what happens between Cathy and Michael as the week’s holiday at the country house goes on.

When discussing how the series might end, all we get out of her is this.

“There’s a feeling of life going on,” she suggests.

“There’s a continuum. And it will go somewhere else which you could make a series about ... but we won’t.”

Mum returns to BBC Two on Wednesday May 15