Just to clarify, Montego Bay was co-written by Bobby Bloom. He was the first artist to record and release the song, in 1970, just four years before his untimely demise in 1974, at the age of 28.
As I mentioned in my original post, Bobby’s 1970 single did well on both sides of the pond, but was actually a bigger hit in the UK (#3) than in the US (#8).
According to this source, cover versions of Montego Bay have been recorded by several different artists and groups over the years. Note that Mungo Jerry is not among those listed.
I’ve searched several Mungo Jerry websites and discographies, as well as YouTube, and can find no evidence of a cover version ever being recorded by Mungo Jerry. That doesn’t necessarily mean that they didn’t do one but, if they did, I can’t find it.
Anyway, Phil identified the song, which is all that’s really required.
Tony, I'm thinking about your latest lyrics. Sorry to say that, so far, they don't sound familiar.