Indigo Girls, O2 Academy, Bristol

It’s interesting to ponder why, after 22 years in the business, the Indigo Girls aren’t more successful or better known outside the cognoscenti and their very loyal fanbase. Their intricate harmonies and beautifully constructed guitar-based folk-rock has attracted many fans (and sometime collaborators) in the music industry - from Natalie Merchant and Ani DiFranco to Lucinda Williams and REM - and one of their albums went platinum. They even won a Grammy, so what’s not to like?

Ah, well there’s the small matter of their political activism - for indigenous peoples’ rights, on green issues and same-sex marriage - for a starter, added to which Amy Ray and Emily Saliers are both gay. If the Dixie Chicks had a tough time of it for an off-the-cuff comment about George W Bush, then for many in the United States the Indigo Girls are beyond the pale. As Ray pithily remarked when there was some mild sexual banter between Saliers and the audience about the word “plectrum”: “We’d best be careful. The next thing you know American radio stations will stop playing our music... Oh, they don’t anyway.’

After 10 albums with Epic, who never really knew how to market these dangerously leftie (by American standards, at least) musos - despite Ray and Saliers being the best acoustic duo since Simon and Garfunkel - the Indigo Girls, from Georgia, have released the excellent Poseidon and the Bitter Bug on their own label IG and now are touring to support it. I saw them last night at the O2 Academy in Bristol and was reminded just how terrific they are live.

Although the album has several musicians providing a rhythm section (there’s a double CD available with acoustic versions as well) at Bristol it was back to basics, with just the two of them on stage, plus a vast array of guitars, a mandolin and a banjolin. They showcased much of the new album, threw in a few old favourites and, of course, the now anthemic singalongs of “Ghost”, “Closer to Fine” and “Galileo”. Every song, old or new, was received with rapturous applause by the markedly diverse audience - teenagers to middle-aged, gay and straight couples in almost equal measure.

But while the new songs were listened to with raptful attention, after each the cries for the old favourites went up anew. Ray and Saliers remained good-natured about this throughout, although the latter was moved to comment at one point: “When you write songs at 19 you sometimes regret recording them.” The requests are understandable, though; the Indigo Girls’ early albums have formed a soundtrack to many a person’s angst-filled teenage or college years and, for their lesbian fans at least, are a musical affirmation of their sexuality.

They kicked off with two songs from Poseidon, “Love of Our Lives”, Saliers’ impassioned rallying call for gay marriage, and “Sugar Tongue”, Ray’s discourse on imperialism and the price we will continue to pay for it for generations to come. If that makes their work sound heavy, it’s not. It's mostly about love and relationships, but they're not afraid to be political about issues that move them, and their lyrics, rich in metaphor and laden with classical and Biblical allusions, are subtlety itself. Saliers’ tend to the poetic and romantic, Ray’s to clearer, even pessimistic, expressions of emotion. On “Sugar Tongue”, by the way, Ray gave a rare run-out to her higher vocal range to a bossa nova beat (and very pleasing it was too) and later on “Yield” played mandolin and made it sound as rock ‘n’ roll as any Fender.

The opening chords of “Get Out the Map”, another oldie, were the signal for the evening’s first singalong. But however they may try, the crowd could never reproduce Indigo Girls’ trademark sound of tight harmonies, a magical combination of Saliers’ fluting soprano and Ray’s deeper counterpoint, on songs such as “Power of Two, “Fleet of Hope” and “I’ll Change”. Added to the vocals is the extraordinary fullness of sound provided by the duo’s dexterity on guitars.

Just two quibbles; the guitar technician was having an off night (the Indigo Girls had to retune several times, which caused the odd hiatus) and the sound wasn’t the clearest mix I’ve ever heard. But no real matter; there were quite beautiful renditions of “Ghost” “Three Hits” and “Closer to Fine” to close. Then an encore of “Second Time Around”, Ray’s song about the importance of staying true to your allies, from the new album. And what else but a rousing singalong of their biggest hit, “Galileo”, to end nearly two hours of superb music.