Probably Southern TV only - it appears to have been broadcast on Tuesdays, not Wednesdays. TV Diaries indicates 13 weeks from 30/6/64-22/9/64 but has no further details www.tvpopdiaries.co.uk/1964.html
Here are a couple of articles from “The Stage” that mention “Discwizz”.
The first one is from 01 June 1964:
Southern want sixty between 15 and 25
Sixty bright youngsters are needed by Southern to appear as pop-music experts. Age limits are 15 and 25 and the main qualification is a lively, intelligent interest in the world of records. Muriel Young and Tony Hall will appear regularly on Discwizz which will be launched on Wednesday, June 24. Each week they will put questions about artists, composers and songs to two teams – three girls in one and three young men in the other. The winning team will get a prize of LP records. Director Mike Mansfield is now looking for the teams. “They need not have appeared on television before” he says. “I want wide-awake youngsters who listen to records and not just hear them, youngsters who take an interest in jazz and ballads as well as the beat scene”. Anyone who would like to appear should write to Mike Mansfield at Southern Independent Television Centre, Northam, Southampton.
This is a snippet from an article about Southern TV from 27 August 1964:
On Tuesday Mark Wynter takes the feature spot in the station’s disc panel show Discwizz. Singer Bobby Shaftoe heads the male panel for the show which is directed by Mike Mansfield and linked and introduced by Tony Hall and Muriel Young.