They are The Lark Rise Band, the locale was the Cheltenham Town Hall, and the event was the Cheltenham Folk Festival 2009 and these are three videos from that performance, and you can't say fairer than that.
Judy Dunlop - Vocals Simon Care - Melodeons, vocals and dancing Ruth Angell - Fiddle and vocals Mark Hutchinson - Guitar and vocals Recorded by Likal - http://www.likal.com(to whom massive thanks go out)