Bill Wells' National Jazz Trio of Scotland aren't a jazz band. Nor are they a trio. Wells formed what was originally an instrumental-based band along with various players from the Glasgow indie scene who had embraced the self-taught composer, arranger, pianist and bass player as one of their own. Wells named his group as a cheeky pop at Scotland's jazz hierarchy unable or unwilling to get that it was okay to look to Brian Wilson and Burt Bacharach as much as Mingus and Monk for inspiration.

The roots of the NJToS Christmas Album date back to the end of 2010, when Wells was invited to curate a night called Black Christmas. A set of what was then described as 'off-kilter covers of Christmas classics' was premiered, with vocals provided by viola player Aby Vulliamy, drummer Kate Sugden and Lorna Gilfedder, previously drummer with Park Attack before singing and playing guitar in Golden Grrrls.

Recorded by Teenage Fanclub's Norman Blake and featuring snow-flake cover art by Jad Fair, the NJToS Christmas Album refreshes twelve seasonal songs in startlingly apposite fashion. By engaging four different singers, including Francois and the Atlas Mountains' Gerard Black, Wells invests seemingly throwaway sing-alongs with a new sense of seriousness and weight that also lays bare the fragile ambiguities of sentiments previously taken at face value.

With Wells playing all instruments apart from Vulliamy's sampled viola, the album's disparate elements go similarly beyond novelty value to make something equally profound. As the sole male presence on the album besides Wells, Black is noted for being the only voice that sounds even vaguely joyful.

The tone is set from the off with Sugden's take on ‘O Christmas Tree’, the sixteenth century German folk tune adopted for communist anthem, ‘The Red Flag’. While another jazz pianist, Vince Guaraldi, played an instrumental version of the tune for the 1965 animated film, A Charlie Brown Christmas, Sugden's delivery is more akin to Robert Wyatt's mournful version of ‘The Red Flag’, released on his Nothing Can Stop Us album in 1982. Here, Wells' keyboards rise and fall with a repeated coda that twinkles in counterpoint to Sugden's vocal.

Gilfedder, Sugden and Vulliamy sing lead on three songs apiece, with Black on two before  a three-woman chorale transforms ‘We Three Kings’ into the sweetest of gender-bending finales. Such quiet subversions point to a sense running throughout the album of Wells sound-tracking something bigger than the songs themselves. These are re-imagined in impressionistically looped swirls that suggest as much darkness as light. On ‘God Rest Ye Merry Gentlemen’ in particular, there's a penetrating sense of menace behind Gilfedder's voice, as if the cherub-faced aliens in The Village Of The Damned had joined the school choir.

‘In The Bleak Mid-Winter’ is already one of the most gorgeous hymns ever written, something accentuated even more by Wells' school assembly piano and Vulliamy's voice on a tantalisingly brief one-verse miniature version. ‘Oh Come All Ye Faithful’ finds Gilfedder's voice wrapped up in Wells' subterranean piano, a sucker punch for the sheer loveliness of We Three Kings and its opaque hints at the odd Steely Dan-ism or Court and Spark-era Joni Mitchell.

Such arrangements never overwhelm an album on which it would have been easy to festoon with kitchen-sink  choirs and strings to score a cross-over hit. Conversely, it's the moody minimalism, both of Wells' stark arrangements and the unstudied precision of the voices, which allows the songs to breathe in a way that lends them an over-riding intensity.

It would be easy to lump the NJToS' Christmas Album in with Nouvelle Vague's series of albums that reinvent contemporary punk classics as playfully constructed retro-chic, but Wells and co are doing something deeper. There are instrumental echoes here of Bernard Herrmann and even John Barry at play, while the purity of the voices recall the likes of Claudine Longet, the breathy-voiced French singer who released several albums in the 1960s and 1970s while married to crooner Andy Williams before being put on trial after her skier boyfriend was shot dead.

Wells and the NJToS have produced an album of considerable charm that sounds pitch perfect for the next few weeks quieter moments. But once the decorations have been packed away and the now threadbare tree taken down, listen again, and the dark-heart hidden in a bunch of songs you thought you knew backwards is plain to hear. Unlike a lot of presents that end up being thrown out beneath a pile of torn wrapping paper, the National Jazz Trio of Scotland's Christmas Album isn't just be for Christmas. It's for life.