The BBC crime series beat out medical drama Call The Midwife, Netflix sci-fi hit Stranger Things and detective series Vera at the annual award ceremony held at The O2 in London on Tuesday night.
Asked in the show’s winner’s room if she thinks her casting will encourage more storylines starring older females, the 58-year-old actress said: “I do hope.
“I think things are changing and they’ve needed to change for a long time, evolution is slow but we’re catching up.”
She confirmed there will not be another series after their success as she feels the show is complete, adding: “It was a story told as a trilogy which has been a great way to tell a story arch.
“The danger is you carry on and it losses its potency but I think this way it keeps it on top.”
The actress also praised the “calibre of writing” by creator Sally Wainwright and the production team.
She also picked up the best drama performance award later in the evening, seeing off tough competition from her co-star James Norton, Queen Charlotte’s India Amarteifio, Vera’s Brenda Blethyn and Call The Midwife’s Judy Parfitt.
Collecting the award on stage, she said: “Thank you so much for this. I have adored every scene, every moment of Happy Valley and I know I will never forget it.”
Comedian Joel Dommett kicked off the show by introducing some of the nominees before he told the audience: “My wife is actually nine months pregnant, she is due basically now.”
He joked that if his partner, Hannah Cooper, goes into labour, Anthony McPartlin and Declan Donnelly are on standby to take her to the hospital.
Reality TV series Gogglebox took home the first award of the night, The Bruce Forsyth Entertainment Award, seeing off tough competition from The Masked Singer and Donnelly and McPartlin who were nominated for two of their shows, I’m A Celebrity… Get Me Out Of Here! and Saturday Night Takeaway.
BBC’s The Traitors also received the award for best reality competition and The Graham Norton Show won in the new TV interviews category, beating Piers Morgan Uncensored on Talk TV, Louis Theroux Interviews… and The Chris & Rosie Ramsey Show to claim the prize.
Norton appeared on a video link to collect the award, saying: “I’m so sorry I can’t be there. Finally, I win a National Television Award and I’m not there.”
He added: “This award, winning it means so much. Mostly it means that Ant and Dec don’t have a talk show… yet. Don’t do it to me, boys.”
The Our Dementia Choir delivered a moving performance during the show, with This Is England actress Vicky McClure admitting she was “shaking” during it.
McClure, who is the founder of the choir, told the audience: “I am shaking through pride that I am feeling right now to witness Our Dementia Choir playing at the O2.”
She added: “Our mission is to share knowledge, raise awareness and aid research to help find a cure, but also to remind everyone that with the right hearts and minds you really can change people’s lives for the better.”
Earlier in the evening, Sir Lenny Henry said “there’s a lot of change happening” in the TV industry with regards to diversity, but said that “the fight… is something that’s ongoing”.
Speaking to the PA news agency on the red carpet at the NTAs, the 65-year-old actor said: “Things are changing.
“We’re seeing more people of colour wielding clipboards and telling people what to do.
“I see more people with disabilities doing stuff, I see more people with tattoos.
“I think there’s a lot of change happening, just in the last five years but, don’t let anybody be thinking that it’s over.
“Because the fight and, it is a fight, is something that’s ongoing.”