Following up Sol's question, and sticking to post-1950 songs:

I'm Looking for a Job
Seven Nights and a Sunday
The Rolling Hills of the Borders
The Foreman O'Rourke
The Freedom Come-All-Ye
The Jeely Piece Song
Star of the Bar
Norland Wind
Both Sides the Tweed
Come by the Hills
My Love Has Gone
Women of Dundee
Generations of Change
far too many interminable Eric Bogle and Brian McNeill things
The Moving On Song
Shoals of Herring
The Terror Time

the last three being the only MacColl songs I've heard sung more than once. Most of those have a clear political message.