So the story goes that PM was enjoying cruising the Caribbean consuming large quantities of grass and got pulled over and warned by US Coastguard. The boat owner wouldn't let him use the boat again ("captain fears there'll be a bust") so rather than curtail their illegal activities the McCartneys found someone less fussy to hire another boat from, a boat called Wanderlust ("help us to be free"). I like the song more now I know it's a subversive drugs song.
Lets see heavy snare, beautiful piano intro and first verse, then later with brass and no Glimour soaring guitar solo: nope not "No More Lonely Nights". It is built around the same melodic theme as that song.