Martin Carthy had a misunderstanding with Paul Simon about "Scarborough Fair," but later cleared up the disagreement.
https://www.telegraph.co.uk/culture/4722968/Friends-again-with-Paul-Simon.html

Davy Graham composed the guitar piece "Anji," or "Angie,", which was later recorded by Paul Simon and others. Don't know if there was a disagreement on that one.

As for Dylan, I don't know of any UK musicians who accused him of expropriation, but Jean Ritchie sued Dylan for his copyrighting of "Nottamun Town." Ritchie claimed it was a traditional song that had been in her family for generations - and she won.

-Joe-