NORTH Eastern folk sisters The Unthanks are to release a new album, Mount The Air, on February 9.

This will be followed by Rachel and Becky's longest British and Irish tour, whose 21 dates will include two Yorkshire gigs: Sheffield City Hall on February 28 and Leeds Irish Centre on March 10, each performed with a ten-piece ensemble.

Two years in the making, Mount The Air has been introduced by the release last month of the title track as a single in "an arresting revision" of the audacious ten-minute opening

piece that has has echoes of Miles Davis and Gill Evans, in their Sketches of Spain period, and climaxes with a burst of euphoria reminiscent of Arcade Fire or Elbow.

Written by pianist, producer and Rachel's husband, Adrian McNally, the song is based on the themes of a one-verse traditional ditty, found in a book of Dorset songs in Cecil Sharp House by Becky, who subsequently co-wrote some of the words with McNally.

The recording features trumpet player Tom Arthurs, a former Elysian Quartet collaborator, now immersed in the Berlin improv scene, while the promo video was made by animator Nick Murray Willis, who was invited on to a BAFTA judging panel on the strength of his video for The Unthanks' Last in 2011.

The album was the first to be made in The Unthanks' makeshift studio in Northumberland, set up in an old granary building 200 yards from where Rachel and Adrian live.

While Mount The Air has the hallmarks of a band working in heightened isolation, since releasing the album Last in 2011 The Unthanks have in fact collaborated with Orbital, Portishead's Adrian Utley, Lau's Martin Green, Martin Hayes, The Voice Squad, Sting, Charles Hazlewood, The Moulettes and German composer Werner Cee.

During that time, they produced a film soundtrack and an orchestral-scale commission for a brass band collaboration with the Brighouse and Rastrick Band.

In addition, they explored The Songs Of Robert Wyatt and Antony & The Johnsons on an album and undertook a First World War project with fellow folk musician Sam Lee, A Time And Place, as well as completing a children’s song commission.

Op top of all that, Rachel and Adrian had two sons and Becky got married.

Now established in the folk firmament, The Unthanks can name Elvis Costello, Robert Wyatt, Ben Folds, Ryan Adams and Rosanne Cash among their devotees.

The latest name to join that list is The Hobbit and Fargo star Martin Freeman, who says: "All I can say about the Unthanks is that they make my heart beat faster, or smile a lot, or cry. They mean it. And not in some dreary 'authentic' way that feels like a penance for the listener, but just natural. They sing and play what the hell they like, and if you've heard nicer harmonies, I may call you a liar. I'm glad to be around at the same time as them.”

The Unthanks have issued Mount The Air independently through their Rabble Rouser Music imprint on CD, download and double vinyl.

Hear the results in Sheffield next month or Leeds in March; box office, Sheffield, 0114 278 9789 or sheffieldcityhall.co.uk; Leeds, 0113 248 0887 or leedsirishcentre.co.uk