Was it clear yet at the time that Corbyn was a tankie crank? If so probably Alliance.
He was known to be very much on the left of the party and a close associate of Tony Benn, but apart from that I don't think some of his more "interesting" views on the world were widely circulated.
Michael O'Halloran, btw, is recalled as one of Labour's less high powered (shall we say) MPs - back in the run-up to the 1975 European referendum he had the unique distinction of signing separate EDMs that both supported and opposed the UK's continued membership