THIS is being billed as Rachel and Becky Unthank’s first studio album since 2011’s Last.

In the meantime, there have been the Diversions records, a bravura series that has taken in Robert Wyatt and Antony and The Johnsons covers, recordings with the Brighouse and Rastrick Band and songs from the shipyards.

No folk group stretches its boundaries more than the Unthanks and that spirit of adventure pays off on Mount The Air, whose opening title track owes much to the jazz of Miles Davis and Gill Evans.

That it features trumpet player Tom Arthurs, part of the Berlin improv scene, tells you everything of The Unthanks’ pioneering ways, driven forward by Rachel’s husband, Adrian McNally, the band’s pianist and innovative musical arranger.

Mount The Air is one of two ten-minute numbers among the 11 here; the other, Foundling, is even better.