The "London Cast" was an unusual, failed experiment for Columbia records.
They had Larry Kert go into a studio and record all of Bobby's songs and lines, then they spliced them--literally!--into the New York cast album.
Nowadays they would do it electronically, the way Natalie Cole sang with her father, and it would be seamless.
That's why the "London Cast" album sounds so lifeless. But trust me, Larry Kert was heartrending as Bobby.
I also saw him do a cabaret act shortly before he died too young, and in the national tour of La Cage with Harvey Evans. It was amazing to see that show with two out proud gay men, as AIDS was taking away so many friends.
What a talent.