I found this interesting and lively footage of Speakers’ Corner in London, filmed during Autumn 1986: https://www.youtube.com/watch?v=dqlXbJOpYiI
A SPGB speaker features right at the start, around 2.5 minutes in and at 9 minutes 50. It’s Harry Young with Steve Ross holding copies of the Standard, as clarified by Dave C in the comments.
The film focuses as much on the hecklers as the speakers, with the one called ‘Irish Jim’ in the comments being the most entertaining (certainly more than our heckler…)