Wonderful post GSS! I posted about John Seymour back in 2009...here's the final paragraph..

...Subsequently Bob (Copper) spent some time with John over in County Wexford and subsequently wrote up the experience in a short and hilarious monograph 'The Irish Papers'. The two of them, both in their late seventies had the time of their lives singing drinking sailing and fishing the River Barrow. One evening John produced a battered old melodeon and commenced singing some familiar East Anglian songs. Bob remarked that he knew them from the renowned Bargeman Bob Roberts (coincidentally also a friend of his)...
"That's where I learnt them" said John, "and this is his instrument. Bob was a dear friend and I sailed on the Cambria with him many times"...and I guess that prompted at least another hour's reminiscing.

I never knew there was any film of him playing.