Paul McCartney held his end of world tour party at the Cavern Club. For the people who came to the door of the Cavern Club that night, the poster on the door told them it was a private retirement party. Little did they realise that Paul McCartney was downstairs.
The following day Paul performed to an audience of 30,000 on an outside stage at King’s Dock.
(The page mentions May 31, when other sites refer to May 30)
From norwegianwood.com:
Sir Paul McCartney went back to his roots by playing a secret gig at Liverpool’s Cavern Club. An audience of 180 close family and friends were at the one-off show. Pregnant wife Heather danced as Paul joined the band Love Train on stage for a set including versions of We Are Family and Let it Be. Cavern owner Bill Heckle said: “He was dancing the night away and enjoyed every minute“.