Second "Big Rock Candy Mountain" even if you have to substitute some words--I think we used to sing "lollipop" for "cigarette" and things like that just to keep the protective types happy.

My brother and I were sold on "Jesse James" and "Captain Kidd" as they appear on the New Golden Ring recordings--not too long, they involve outlaws, and they have active story lines and fairly lively tunes. I don't know what a good UK equivalent would be--maybe "Brennan on the Moor" instead of "Jesse James".

"A Fox Jumped Up On a Chilly Night" is also a pretty good one; it's about animals and has some repetitive lines that kids could learn quickly and join in.

"Aiken Drum", "Elmer and the Bear", and "Tell My Ma" also come to mind.