The instrument that you saw at Whitby was a prototype MIDI concertina being played by Bill Whaley to accompany his singing partner Dave Fletcher. And that would have been about 3 years ago when they played for the Folk Festival service.
That prototype instrument has now developed into the S-Wave Instruments E64 English MIDI Concertina with the result that the 'Purple People Pleaser', as it became known, has been retired and Bill is now playing a production instrument. This instrument has been mentioned in a number of threads in this forum but if you wish to know more then please visit the S-Wave Instruments website at http://www.s-wave.co.uk.
If you wish to know more about Bill and Dave then their website can be found at http://www.whaleyfletcher.co.uk.
Oh yes, I'm not claiming that this was the first MIDI concertina either, as I have heard tales of one or two previous attempts to MIDI-fy concertinas, although I don't know if these ever made it on to a stage.
Dean Onyon