The Socialist Studies website has a link to a youtube channel which features 8 videos of Edgar Hardcastle speaking on Marxian Economics. These date from when he was a member of the SPGB.
https://www.youtube.com/channel/UCXq0kw9sU6xvrr34yezA_Tw
The videos have been transferred from video cassette and probably date from 1986. I have an old list of Party videos which gives a date of 1986 for a series of five lectures from July to September of that year.