As reported by The Digital Bits,

Finally, we’ve learned from industry sources that the 4K Ultra HD release of James Cameron’s The Abyss (1989) in the UK has been cancelled, and for exactly the reason you think—the scene in which the rat is made to breath underwater. UK censors asked for the scene to be cut, Disney apparently wanted to comply, but Lightstorm vetoed it. So if you want this title in 4K and you live in the UK, you’ll have to import it from elsewhere.

For those who don’t know the history, the RSPCA (The Royal Society for the Prevention of Cruelty to Animals) made a complaint about the scene where the rat is forced to breathe the oxygenated liquid.

Despite James Cameron protesting that no rats were harmed in the making of the film, the BBFC upheld the complaint and the scene is cut in the UK.

I first saw the film on television, where the station accidentally broadcast the uncut version, so I was very surprised to find the scene cut when I purchased my copy of the Special Edition on VHS.

The scene in question is sloppily edited using alternate footage in a quality vastly different to that of the rest of the film and, if I remember correctly, the aspect ratio changed as well!

Yes, this news has annoyed me but at the end of the day, it’s a region free 4K disc, and I’ll simply import from a neighbouring country.