Police had to intervene as a scuffle broke out moments after Labour shadow chancellor John McDonnell's re-election was confirmed.
Footage from the Hayes and Harlington count, in Uxbridge, West London, showed angry exchanges between a handful of people.
Cries of "liar" rang out as Mr McDonnell was giving his acceptance speech. Police had to intervene to deal with the disturbance.
In his victory speech, McDonnell said:
Several people with lanyards on had to be pulled apart, with bystanders capturing the incident on mobile phones.
Speaking afterwards, Mr McDonnell said: