Glug was in the development at Rare at one point, a game idea by Paul Proctor, a guy with quite a game "track record". It was resurrected from some old dev disks by game development veteran Kevin Edwards.

As promised here is a video of NES GLUG by Paul Proctor which I rescued recently from his development disks. This is the first time this has been seen by anyone apart from a few close friends and the Stampers at RARE. His disks were in a bad state and needed a deep clean. It's an early development build. SFX / music not implemented. Only two maze designs done. Probably about 60-70% complete. Kevin Edwards (on X)

I remember asking the Stampers about Glug. They had a folder on a shelf with GLUG on it but they wouldn't let us look inside. They said it was a game that was amazing but the hardware good enough yet. Fascinating to actually see it. John Pickford (on X)

That is pretty much all the information available about Glug at the time of writing, the game was never announced.