Вот, кстати, информация про него и саму песню:
https://en.wikipedia.org/wiki/Yma_o_Hyd
https://en.wikipedia.org/wiki/Dafydd_Iwan
Там же про партию, например: "From 2003 to 2010, Iwan was the president of Plaid Cymru, a political party which advocates for Welsh independence from the UK".