Penning tunes had always come easy to the country-folk superstar, but after being faced with a political climate she didn't agree with, as well as recovery from thyroid and breast cancer (which she was diagnosed with in the late Nineties), it became a proper struggle. "It lasted through the Bush administration," says Griffith, who comes to the Queen's Hall on Sunday night. "The direction the country went in for four years led me into severe depression and my pen went into the sand. The election (of Barack Obama] brought out the acceptance of hope and a new direction. When I went to Europe, I wasn't embarrassed about my country. It opened up hope and allowed me to take my pen out of the sand." For Griffith, who only this week received a lifetime achievement award at the BBC Radio 2 Folk Awards, suffering the dreaded writer's block was a shock to the system. "I'd never had any kind of block before – I was always prolific," she says. "As I matured, I edited myself. But this was very depressing and I didn't have a clue how to get out of it." But get out of it she did – "after the 2008 election, everything came spilling out". She explains, "Things came along like the Mildred and Richard Loving case. That was such an inspiration... just wondering why I never knew about this and how important that case is currently with equality in marriage." More of them later. First, Griffith got an early start on her path to songwriting, starting to write her own songs at the age of six, which she thought of as part of the process of learning how to play the guitar. And while she doesn't remember many of her earliest songs, she does recall that "the first original song my mother commented on was a song about (60s acid guru] Timothy Leary." Then, at the age of 14, when a campfire turn at the Kerrville Folk Festival caught the ear of singer Tom Russell, she was on her way. Fast forward to today, and with a mantelpiece full of awards to show for her efforts, it's safe to say she's never looked back. As you'd expect from an artist whose creativity was reignited by changes in American politics, The Loving Kind is Griffith's most politically outspoken release in years, and underscores her stature as one of the music world's most esteemed singer-songwriters. "It was nice to focus on things outside of my body – and music has always done that for me," explains the singer, whose best work echoes the women who came before her, such as Joni Mitchell, Janis Ian and Joan Baez. Perhaps the most striking song on her new album is Not Innocent Enough – a poignant statement against the death penalty. It deals with the story of Philip Workman, who was accused of killing a policeman and convicted – with tainted testimony. "I started writing this long before Philip was executed but just could not finish it until that final injustice took place," explains Griffith. "I am a total abolitionist on the death penalty. I just hope (the song] makes a difference." Also dear to Griffith's heart is the song Cotton's All We Got. "I always wanted to write something to remind people that LBJ (Lyndon B Johnson, president of the US from 1963 to 1969] was so much more than just the Vietnam War. He was a huge heart dedicated to his country and social reform." Elsewhere on the album, Sing is an autobiographical ode to expression and inspiration. Griffith explains, "I was actually inspired to write that by watching an interview with Shania Twain where she said it would not have mattered if she remained a lounge act for her whole career. "Artists don't choose to be artists, writers or singers. It's just something you know you have to do." As well as a great songwriter, Griffith is a great interpreter of other artists' songs. The Loving Kind features four outstanding covers – Party Girl, Tequila After Midnight, Money Changes Everything, Pour Me a Drink. It's arguably the title track, the aforementioned true story of how love triumphed over a social injustice that prevailed in the US until 1967, that's closest to Griffith's heart. For those unaware, Mildred and Richard Loving were a mixed-race couple who were put in prison when they married in 1958, but their case eventually reached the Supreme Court, where state laws against interracial marriage were struck down. "I read Mildred Loving's obituary in The New York Times and it just floored me," says Griffith. "She never remarried after Richard died and in her last interview before she passed she expressed hope that their case, Loving v. Virginia, would eventually be the open door to same sex marriage." Like the best folk singers, true stories have always worked their way into Griffith's songwriting. "In some ways, I'm just a journalist," she says. "I want my audience to hear these stories." Nanci Griffith, Queen's Hall, Clerk Street, Sunday, 7pm, 28, 0131-668 2019