TO BE 74 years old is no longer to be ancient. Yet Liam Clancy, sole remaining member of The Clancy Brothers and Tommy Makem, does seem a little like a figure from the Pleistocene era.

In the early 1960s, before Dana won the Eurovision and Jim Sheridan secured an Oscar nomination, we treasured our few famous Irishmen, and none was better known than the ballad singer from Carrick-on-Suir. In the decades since, however, the Clancys’ apparent embrace of stage Irishness (those jumpers) has somewhat obscured their charisma and talent.

The time is right for a reappraisal. Alan Gilsenan, one of Ireland’s most distinguished documentarians, has spent the past four years assembling material on Clancy. The result, though overlong, goes some way towards confirming his subject as a national treasure.

Positioned in a vast darkened space, images of significant figures appearing over his shoulder, Liam Clancy holds forth with the same gusto he used to direct at ballads and rebel songs.

Raised in a traditional family, Liam was lured to New York by Diane Guggenheim, heiress to the fortune that bears her name, and propelled into one of the great 20th century Bohemias. Following a distinctly uncomfortable incident – Guggenheim became sexually obsessed with the young fellow – he and his brothers set about flogging a particular class of Irishness to the world. The usual rock’n’roll traumas followed: girls, booze, breakdown, personal differences.

Gilsenan has tracked down an impressive number of secondary sources, and his use of other performers’ music is often inspired. It is, however, Liam Clancy’s resonant voice – speaking, singing, laughing – and his remarkable gift for structuring a good story that allows the documentary to soar.

The Yellow Bitterndoesn't quite manage to make the Clancys hip, but it establishes the last upright member as a serious figure with a remarkable tale to tell. We owe it to him to listen.