An important expectation for the UK viva is that it is private. Members of the public don’t attend and you’ll never have an audience present while you talk with your examiners.
Two examiners, one internal and one external, is the typical situation at the UK viva. It’s possible to have more, but rare. It’s possible to have an independent chair as part of your viva process, but they’re not an “audience member” either.
Your supervisor could attend, with your permission, but even then they are not like an audience member. They can only observe, they can’t participate like an audience member at a public thesis defence.
The UK viva is a discussion, not a presentation, not an open forum. It’s closed, and even if there are others present – chairs or supervisors – they’re not the audience.