If Ewan was a deserter, why was he never prosecuted?

The song was written in reference to Salford, then in Lancashire, now in Greater Manchester, England, and the place where Ewan MacColl was brought up. When he first wrote the song, the local council were unhappy at having Salford called a dirty old town and, after considerable criticism, the words of the song were changed from "smelled a Spring on the Salford wind" to "smelled a spring on the smoky wind"

BTW what canal do we think he is referring too, we have a choice of two, M/cr Ship or Bridgewater canal?