sorry but the oliver cromwell suggestion is completely wrong. the writer was clearly not english and oliver cromwell is one of the few olivers commonly taught about overseas. anyways, the oliver is question is oliver churchill, brother of winston. Oliver Churchill was a politician as well and heavily influenced social matters in the UK years ago. The song is about his policy of giving jobs to those who are unemployed by making them soldiers. People were unable to recieve dole(welfare) if they were eligible to join the military and didnt. Britain was pretty much building up their army and sending soldiers all over the place to solve unemployment. This is what olivers army is about.
"called careers information, have you got yourself an occupation?"
"But there's no danger. It's a professional career, though it could be arranged with just a word in Mr. Churchill's ear.If you're out of luck you're out of work
We could send you to Johannesburg"