Sam Lee sang with Jon Boden for On Christmas Day, a duet which he normally performs with a temporarily voiceless John Spiers, and this was undoubtedly unrehearsed (I haven't seen it but I did hear it, and well done Sam). And Jim Moray depped for Benji Kirkpatrick who was unable to be at the recording. What this demonstrates is how versatile and skilled English trad musicians are, over and above many another genre. Though Joe Public wouldn't be aware of this and those Good Enough For F*lk carpers from the Swiggin' Pig who proudly proclaim unawareness of the artists involved wouldn't care.