I work by my own ideas re: 'what is folk' and, to me, a folk song *might* be composed by a known person but it isn't folk until it becomes part of a popular community based repertoire. Until then, it's just singer-songwriter stuff. And, as I said, that's my personal yardstick so I'm not going to argue the toss.

The song that, although no longer topical, is still being sung goes to the tune of Camptown Races:

Pwy yw'r Heddlu methu'u dal?
Meibion, Meibion,
Pwy yw'r Heddlu methu'u dal?
Meibion Glyndwr.

Meibion Glyndwr! Meibion Glyndwr!
Pwy yw'r Heddlu methu'u dal?
Meibion Glyndwr.

trans:
Who are the Police failing to catch?
Meibion Glyndwr.
etc.

Meibion Glyndwr being the identity assumed by those who were busy burning holiday cottages in rural Welsh communities in the 1970s/1980s. This song surfaced in late night pub sessions in NW Wales in the 1980s.

You did say UK. I'm assuming that if you meant 'English' you would have said 'English'.

There are a lot of political-edged singer-songwriter / accoustic songs in the Welsh language that would probably fit your parameters. I like "Meibion" because it just sort of appeared ... and so was very 'folk'.

sian