The Pet Shop Boys, Astoria, London

The Pet Shop Boys have stripped down. Previous live shows were costume-changing carnivals, alive with mischief and tongue-in-cheek theatrics; the present spectacle is an altogether more sombre and mature affair. The failure of last season's musical, Closer to Heaven, seems to have left Chris Lowe and Neil Tennant chastened and possibly a tad dispirited. Their current "Uni Tour" hosts a back-to-basics (or at least Eighties-interior) design and features a cognoscenti-pleasing set-list comprising some less-celebrated selections from their catalogue and previously untested material from their forthcoming album, Release.

Seated behind his centre-stage keyboard console, the baseball-capped Lowe leads the percussionist and guitarist into the busy techno groove of "Disco Potential". When Tennant arrives on stage, even the live instruments sound like a machine – aptly so, as the lyric wryly comments on Simon Cowell and his production-line-pop ilk.

Tennant's portly bulk, clad all in black, and grey temples mark him out as an aged contender in the Pop Idol stakes. As he strums on an acoustic guitar for the first new song, "I Get Along", the tag-line, "I get along without you very well", could be aimed at the deserting masses. The turgid melody has a funereal cast, and though that is partly dispelled by the magical "Love Comes Quickly", which follows, the downbeat, lacklustre feel emerges too often for comfort.

It's the new material that proves most problematic. Whereas the Pet Shop Boys were once imperiously perched above the oddities and aberrations of pop culture, there's now a dutiful sense of salesmen flogging their new, patently substandard wares. The show is a jarring mix of high-spirited peaks (their irrepressible debut, "West End Girls") and sagging, mournful troughs (the listless ennui of the new "Birthday Boy").

The crowd hears it differently, receiving the gushing and over-dramatic "Love Is a Catastrophe" as an honest expression of emotional turmoil. Perhaps it's unfair to invoke the old adage "Being natural is the biggest pose of all", but it's when in sharp and rude form that Tennant is at his best. The glitzy, uptempo cheek of "Sexy Northerner" and the bucking-bronco beat of "New York City Boy" – with the front man slapping his leather-clad thigh to much wolf-whistling – charge the crowd with a celebratory atmosphere.

But the need to balance the blitzing pop moments with more poignant, personal expression is pointedly illustrated by the encores. The riot of air-punching and foot-stomping that accompanies the old standby "Go West" gives way to the dolorous "You Choose", an insular and almost aggrieved farewell. In their 18th year, the Pet Shop Boys are a reminder that survival in pop music can be just as hard for ageing stars facing mid-life crisis as it is for wannabe Pop Idol contenders.