I had heard of The Oppositionist mentioned in the same breath as early 1970s British Left-Communist or Councilist formations but, from a reading of the one issue we have from 1974, it is difficult to place the group producing it directly within those traditions.

The articles on votes for women is not typical left-communist fare and the articles on Portugal and a long discussion on the theory of Permanent Revolution could indicate an origin within the Trotskyist movement- perhaps the International Socialists- or maybe Solidarity.
Similarly the article on the role of the revolutionary socialist newspaper, which critiques Workers Press and Socialist Worker and calls for a paper written by and aimed at workers, points in that direction.As it says of itself, this article (reprinted from an earlier issue of Oppositionist) is a critique of both Marxist and Libertarian groups.
The “Where We Stand” page fuses a state-cap analysis of the USSR with calls for workers control (?self-management), a rank and file approach in the trade unions and elements which seem to lean in an autonomist direct…
Oppositionist ran between at least 1971 and 1974 (this issue). There are a couple of named individuals in the paper (possibly pseudonyms) but I do not recognise either of them- Ed Russell and Carl Wakeling.
It would be good to track down other issues of this paper. I am visiting Bishopsgate in March and may find them there.
The Sparrows Nest holds a pamphlet (not yet digitised) which seems to be the same group:
Ciliga, Anton. Revolutionary Politics in Stalin’s Prisons :.
Series,Volume,Issue: (Oppositionist Pamphlets, , ). Publisher: (Oppositionist, , London, England, UK/, Dec 1974).