See, in the DT:

CADGWITH ANTHEM  Text and tune. No source specified for either.

BEAUTY OF KASHMIR  Much shorter text from a Steeleye Span record. No tune given or previous source named.

COME FILL UP YOUR GLASSES (Robbers)  The same short text, this time a bit oddly spelled, from the same Steeleye Span record. No tune given or previous source named.

In the Forum:

Lyr req: Caves/Beauty of Kashmir  -includes some speculation on "the beauty of kashmir / cashmere".

Peter Kennedy recorded the song from the Cadgwith Fishermen's Choir in 1953; Steeleye Span appear to have recorded an arrangement based on that, though they don't seem to have bothered to credit their source. Whether it's a particularly old song I don't know, but on the whole I doubt it.