It’s definitely in both the book and the movie, exact same line -
“Soon we may be needing all our prison space for political offenders.”
As stated by the Minister of the Interior or Inferior.
Alex was the first test subject, but if he was successful, they were absolutely planning on using the technique on many more prisoners. That’s why they had the whole scene where they demonstrate to an audience of VIPs how effective the treatment was.
However, the bit I mentioned above where Alex and his cellmates kill a new prisoner is not in the movie, just the book.
