In the run-up to Red Nose Day, Ramsgate-born actress Brenda Blethyn stars in a one-off drama about malaria, Mary & Martha, which was written by Richard Curtis and airs on BBC1 on Friday, March 1. The actress talked to Susan Griffin about working with co-star Hilary Swank, visiting Uganda and how she felt about landing the role because she's "so ordinary".

Brenda Blethyn couldn't have been happier when her agent rang to say Richard Curtis wanted to send her a script.

"I thought 'Yippee!'" says Blethyn of the writer and film-maker behind such hits as Bridget Jones, Notting Hill and Love Actually.

Renowned for his idyllic and funny movies, you can forgive the Bafta and Golden Globe winner's surprise when she discovered the subject matter at the heart of Mary And Martha.

A powerful 90-minute film, it tells the story of two very different women who are brought together when both their sons die from malaria in Africa.

"This one was a bit of a departure but it was a nice surprise," says the actress, looking glamorous in dark trousers, yellow top and blue jacket.

"I was very moved by the script, went to meet Richard and straight away wanted to do it."

Her co-star is the American actress and two-time Oscar winner Hilary Swank, who Blethyn first met at Swank's home in North Carolina.

"We turned up for rehearsal at her house and we were talking about acupuncture. I'm sceptical about it, she's a fan," laughs the down-to-earth 66-year-old.

The story sees Mary (Swank) take her young son George to Africa with the promise of adventure and fun, when he contracts the disease, while Martha's son, Ben (Sam Claflin), dies while working as a volunteer in Mozambique.

Heartbreaking and uplifting all at once, the film follows Mary's return to America, where she begins a one-woman campaign to raise awareness of the disease, while Martha volunteers at the orphanage where Ben worked.

"She's compelled to go there and see where he lived and worked and see if there's a footprint, the smell of him, something he's touched, just something since she last saw him," explains Blethyn.

When the new volunteer turns up to take her son's place, "it's like a stab in the heart for Martha", she says.

"But she realises it's time for her to get out the way. Life goes on and I think she's compelled to take that step and go to America to help in whatever way she can with Mary's campaign."

Directed by Salt's Phillip Noyce, the drama coincides with the run-up to Comic Relief's Red Nose Day on Friday, March 15.

This year marks the 25th anniversary for the charity Curtis founded in 1998.

Since then it has raised millions of pounds for people living in Africa and the UK.

Combining comedy and humanity, the story is Curtis at his best, Blethyn believes.

"It's a remarkable story of the courage, dignity and humour of two very different women in their effort to make the world a better place," she says.

"Just the number of children! More than half a million die every year and it's so affordably preventable. Comic Relief supplied thousands of nets to badly-affected parts of Uganda and the deaths went down by a third."

A few days after our interview she'll be visiting Uganda, a malaria hotspot, in aid of Comic Relief.

"It's new territory for me. I've never done anything like that before and I'm a bit scared," she admits.

"I just hope I don't get sick. I don't want to be bitten and I don't want to see others who have been bitten and mothers who have lost children to malaria, but I'm going."

Although Mary And Martha is set in Mozambique, the drama was filmed in South Africa, a relatively low-risk area for malaria.

"It was winter and it was absolutely freezing cold but we've got to pretend we're in Mozambique, so the director kept shouting [puts an Australian accent on], 'Make-up! More sweat on Martha!'" Blethyn recalls, laughing. "You can probably see us shivering but it was a wonderful experience."

Not least because of working with local children. "Not all the children were orphans but there was a village very nearby where there were over a thousand children who are all orphans," she says.

"It was emotional but also uplifting because they're so resilient and so well behaved - and very happy to be taking part."

She only recently finished filming another series of her TV detective show Vera, and after her Uganda trip will have a short time off before flying to New Mexico to shoot Enemy's Way with Robert Duvall and Forest Whitaker.

The film will reunite her with the French director Rachid Bouchareb with whom she worked on the independent film London River.

"When I was working with him, he said [puts on a French accent], 'Brenda what would you like to do?' I said, 'I'd like to do a Western'.

"A month ago he rang and said, 'Brenda, we are going to make movies. I want you in my Western!' I asked if he was sure and he said, 'I want you in my movie because you are so, so... very, very ordinary!'

"I'm flattered because I know what he means. He wants 'real' people," adds Blethyn, who was Oscar-nominated for downtrodden roles in Secrets & Lies and Little Voice.

"I just like characters who aren't pretending to be someone else," she adds.

While her work commitments keep her busy, there's no question she'll continue to work as an ambassador for Comic Relief.

"If they ask me to, I will," she says. "But then I think we all should all be. We should all spread the word."