In the first five months of 1972 there were across the United Kingdom over fifty peaceful protests by prisoners.
[1]: 176 PROP was launched on 11 May 1972 in a public house, the Prince Arthur opposite Pentonville Prison, to "preserve, protect and to extend the rights of prisoners and ex-prisoners and to assist in their rehabilitation and re-integration into society, so as to bring about a reduction in crime.
"[2] PROP's foundation meeting was held in Hull and was attended by 60 people.
Speakers included Norwegian sociologist Thomas Mathiesen, Jack Ashwell local branch secretary of the TGWU and Ros Kane from Radical Alternatives to Prison.
PROP were active for a few years, it's not clear when the organisation closed.