Were there really any songs that MacColl wrote himself but tried to pass off as "traditional"?

I thought quite the oppposite, that a few of the songs he acknowledged writing from the start were later thought to be "traditional" by others.

"Shoals of Herring" is the prime example. It was quite openly based on quotations from fisherman Sam Larner, but MacColl made a song of them with additional material and a tune I believe he composed.

MacColl often collated texts or otherwise slightly altered them, always with great respect for the originals and always, I think, with an indication of what he'd done.

"The wild and wasteful ocean" line, however, is Shakespeare's.