Fortunately, nothing can be seen in that video, but it gives a vague idea of what happened. As Steve Bray suggests, it may be related to the traffic management around Starmer's motorcade, i.e. it's not clear which lane of vehicles had been released from Bridge Street by traffic signal operation. This will undoubtedly be examined owing to the police operation. If it were found that there was a failure of appropriately directing traffic, it might help the victim.
Fortunately, nothing can be seen in that video, but it gives a vague idea of what happened. As Steve Bray suggests, it may be related to the traffic management around Starmer's motorcade, i.e. it's not clear which lane of vehicles had been released from Bridge Street by traffic signal operation. This will undoubtedly be examined owing to the police operation. If it were found that there was a failure of appropriately directing traffic, it might help the victim.