The London Theatre Orchestra (they record for Hallmark Records)

also credited as The London Theatre Orchestra & Cast (see https://itunes.apple.com/gb/album/phantom-of-the-opera/id307578224 )

it's possible they are also credited by these other names:
The London Stage Orchestra and Singers
The London Starlight Orchestra and Singers - see https://musicbrainz.org/artist/f3cc1743-96c0-40f1-8c0e-766312981ffb
The Starlight Orchestra and Singers - see https://musicbrainz.org/artist/017752f5-4abd-486e-9103-a38f8676c167
The London Westend Singers & The London Theatre Orchestra (see http://www.allmusic.com/album/mw0000264314 )
The West End Orchestra & Singers - see https://musicbrainz.org/artist/8d780703-10c1-42ee-8154-0701e9c749c1 and https://musicbrainz.org/artist/45a42d52-1c59-443f-8de7-30de900ecf4b
The Stage Door Orchestra - see https://musicbrainz.org/artist/9174331e-f610-4a50-a234-0be347aad90d

Also see The Countdown Singers / Madacy. Madacy repackage a LOT of covers and just keep changing the names of their performers. That's if they even name the performers!