"We're ganna do two sets," begins Chas Hodges (the slightly bigger one, piano), taking his place behind the keys. "The second one is abaht the hits, but this is what we were doin' in the 70s."
The 1970s? For anyone under 45, it's hard to think of Hodges and bandmate Dave Peacock (the slightly thinner one, bass) as anything but synonymous with the 1980s, when their "rockney" music – a knees-up blend of rock'n'roll, music hall and boogie-woogie – was the epitome of cheery British light entertainment.
Yet they were always more than a novelty act, with a musicianship and a pedigree that, however implausibly, includes supporting Led Zeppelin at Knebworth festival, playing with Jerry Lee Lewis and Joe Meek (Chas did both, in the Outlaws), and being sampled by Eminem. This rare excursion into their pre-fame secret history shows another side to the much-loved duo: documentarians of a lost England, in the manner of the Kinks. It's hard not to be moved by Edmonton Green's ("abaht me 'ome tarn", explains Chas), stirring lament for a long-gone "rough old gaff" that "still meant a lot to the locals".
Even in their chart-busting heyday, the pair evoked nostalgia for an already fading working-class culture, and the second half revives the duo most fans remember: long-suffering husbands who wore belts and braces, kept their beer in the sideboard, lived next door to each other in back-to-backs (at least, they did in the video for Margate), kept dogs who'd leave a "message" on the carpet and preferred English seaside towns to the Costa Brava ("and that palaver").
Chas's son Nik ably replaces retired drummer Mick Bur, but otherwise they haven't changed. They've certainly never, God forbid, moved upmarket and called themselves Charles and David, or experimented with dubstep (although, after a brown ale or two, you could possibly argue that the pair's quick-fire wordplay pioneered British rap). They parted in 2009 after Dave's wife died, but the more melancholy songs of their recent comeback album are overlooked for songs which Mustn't Grumble.
The large theatre is eventually transformed into a giant boozer as Gertcha, Sideboard Song and "daaaarnnn to Margit" have 'em dancing in the aisles, while Rabbit and a sublime Ain't No Pleasing You become mass sing-alongs. However, That Old Piano, 70-year-old Chas's eulogy to an ageing Joanna, best sums up their own endurance: a national treasure that gives "so much pleasure".
• At ABC Glasgow on 19 April. Box office: 0141 332 2232. Venue: chasndave.net. Then touring.
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